Three-dimensional memory device with composite charge storage structures and methods for forming the same

ABSTRACT

A memory device includes an alternating stack of insulating layers and electrically conductive layers located over a substrate, and a memory stack structure extending through the alternating stack. The memory stack structure includes a composite charge storage structure, a tunneling dielectric layer, and a vertical semiconductor channel. The composite charge storage structure may include a vertical stack of tubular charge storage material portions including a first charge trapping material located at levels of the electrically conductive layers, and a charge storage layer including a second charge trapping material extending through a plurality of electrically conductive layers of the electrically conductive layers. The first charge trapping material has a higher charge trap density than the second charge trapping material. Alternatively, the composite charge storage material portions may include discrete charge storage elements each containing a silicon nitride portion and a silicon carbide nitride liner.

FIELD

The present disclosure relates generally to the field of semiconductordevices, and particularly to a three-dimensional memory device withcomposite charge storage structures and methods of manufacturing thesame.

BACKGROUND

Three-dimensional vertical NAND strings having one bit per cell aredisclosed in an article by T. Endoh et al., titled “Novel Ultra HighDensity Memory With A Stacked-Surrounding Gate Transistor (S-SGT)Structured Cell”, IEDM Proc. (2001) 33-36.

SUMMARY

According to an aspect of the present disclosure, a memory device isprovided, which comprises: an alternating stack of insulating layers andelectrically conductive layers located over a substrate; and a memorystack structure extending through the alternating stack, wherein thememory stack structure comprises a composite charge storage structure, atunneling dielectric layer located on an inner sidewall of the compositecharge storage structure, and a vertical semiconductor channelcontacting an inner sidewall of the tunneling dielectric layer. Thecomposite charge storage structure comprises a vertical stack ofdiscrete tubular charge storage material portions including a firstcharge trapping material located at levels of the electricallyconductive layers and vertically spaced apart from each other, and acontinuous charge storage layer including a second charge trappingmaterial extending through a plurality of the electrically conductivelayers. The first charge trapping material has a higher charge trapdensity than the second charge trapping material.

According to another aspect of the present disclosure, a method offorming a memory device is provided, which comprises: forming analternating stack of insulating layers and spacer material layers over asubstrate, wherein the spacer material layers are formed as, or aresubsequently replaced with, electrically conductive layers; forming amemory opening through the alternating stack; and forming a memory stackstructure by sequentially forming a composite charge storage structure,a tunneling dielectric layer, and a vertical semiconductor channel inthe memory opening. The composite charge storage structure is formed by:forming a vertical stack of tubular charge storage material portionsincluding a first charge trapping material and at levels of theelectrically conductive layers as discrete material portions that arevertically spaced apart by the insulating layers; and forming a chargestorage layer including a second charge trapping material and extendingthrough a plurality of electrically conductive layers of theelectrically conductive layers.

According to an aspect of the present disclosure, a memory device isprovided, which comprises: an alternating stack of insulating layers andelectrically conductive layers located over a substrate; and a memorystack structure extending through the alternating stack, wherein thememory stack structure comprises a vertical stack of discrete chargestorage elements that are vertically spaced apart from each other andlocated at levels of the electrically conductive layers, a tunnelingdielectric layer located on inner sidewalls of the discrete chargestorage elements, and a vertical semiconductor channel contacting aninner sidewall of the tunneling dielectric layer, wherein each of thediscrete charge storage elements comprises: a silicon nitride portionincluding an inner sidewall that contacts an outer sidewall of thetunneling dielectric layer; and a silicon carbide nitride liner incontact with the silicon nitride portion.

According to another aspect of the present disclosure, a method offorming a memory device is provided, which comprises: forming analternating stack of insulating layers and sacrificial material layersover a substrate; forming a memory opening through the alternatingstack; forming annular recess regions around the memory opening atlevels of the sacrificial material layers; forming discrete chargestorage elements in the annular recess regions, wherein each of thediscrete charge storage elements comprises a silicon nitride portion anda silicon carbide nitride liner disposed between the silicon nitrideportion and a respective one of the sacrificial material layers locatedat a same level as the silicon nitride portion; forming a tunnelingdielectric layer, a vertical semiconductor channel, and a drain regionin the memory opening; and replacing the sacrificial material layerswith electrically conductive layers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic vertical cross-sectional view of a first exemplarystructure after formation of at least one peripheral device and asemiconductor material layer according to a first embodiment of thepresent disclosure.

FIG. 2 is a schematic vertical cross-sectional view of the firstexemplary structure after formation of an alternating stack ofinsulating layers and sacrificial material layers according to the firstembodiment of the present disclosure.

FIG. 3 is a schematic vertical cross-sectional view of the firstexemplary structure after formation of stepped terraces and aretro-stepped dielectric material portion according to the firstembodiment of the present disclosure.

FIG. 4A is a schematic vertical cross-sectional view of the firstexemplary structure after formation of memory openings and supportopenings according to the first embodiment of the present disclosure.

FIG. 4B is a top-down view of the first exemplary structure of FIG. 4A.The vertical plane A-A′ is the plane of the cross-section for FIG. 4A.

FIGS. 5A-5M are sequential schematic vertical cross-sectional views of amemory opening within the first exemplary structure during formation ofa memory stack structure, an optional dielectric core, and a drainregion therein according to the first embodiment of the presentdisclosure.

FIG. 6 is a schematic vertical cross-sectional view of the firstexemplary structure after formation of memory stack structures andsupport pillar structures according to the first embodiment of thepresent disclosure.

FIG. 7A is a schematic vertical cross-sectional view of the firstexemplary structure after formation of backside trenches according tothe first embodiment of the present disclosure.

FIG. 7B is a partial see-through top-down view of the first exemplarystructure of FIG. 7A. The vertical plane A-A′ is the plane of theschematic vertical cross-sectional view of FIG. 7A.

FIG. 7C is a schematic vertical cross-sectional view along the verticalplane C-C′ of FIG. 7B.

FIG. 8 is a schematic vertical cross-sectional view of a region thefirst exemplary structure after formation of source regions according tothe first embodiment of the present disclosure.

FIG. 9A is a schematic vertical cross-sectional view of the firstexemplary structure after formation of backside recesses according tothe first embodiment of the present disclosure.

FIG. 9B is a schematic vertical cross-sectional view of a region thefirst exemplary structure of FIG. 9A.

FIGS. 10A-10C are sequential vertical cross-sectional views of a regionof the first exemplary structure during formation of electricallyconductive layers according to the first embodiment of the presentdisclosure.

FIG. 11A is a schematic vertical cross-sectional view of the firstexemplary structure after removal of a deposited conductive materialfrom within the backside trenches according to the first embodiment ofthe present disclosure.

FIG. 11B is a partial see-through top-down view of the first exemplarystructure of FIG. 11A. The vertical plane A-A′ is the plane of theschematic vertical cross-sectional view of FIG. 11A.

FIG. 11C is a vertical cross-sectional view of the first exemplarystructure along the vertical plane C-C′ of FIG. 11B.

FIG. 12 is a schematic vertical cross-sectional view of the firstexemplary structure after formation of an insulating spacer and abackside contact structure within each backside trench according to thefirst embodiment of the present disclosure.

FIG. 13A is a schematic vertical cross-sectional view of the firstexemplary structure after formation of additional contact via structuresaccording to the first embodiment of the present disclosure.

FIG. 13B is a top-down view of the first exemplary structure of FIG.13A. The vertical plane A-A′ is the plane of the schematic verticalcross-sectional view of FIG. 13A.

FIGS. 14A-14K are sequential schematic vertical cross-sectional views ofa memory opening within a second exemplary structure during formation ofa memory stack structure, an optional dielectric core, and a drainregion therein according to a second embodiment of the presentdisclosure.

FIG. 15 is a vertical cross-sectional view of a region of the secondexemplary structure after replacement of the sacrificial material layerswith electrically conductive layers and removal of a depositedconductive material from within the backside trenches according to thesecond embodiment of the present disclosure.

FIG. 16 is a vertical cross-sectional view of a region of the secondexemplary structure after formation of backside contact via structuresaccording to the second embodiment of the present disclosure.

FIG. 17 is a vertical cross-sectional view of a memory opening within analternative configuration of the second exemplary structure afterformation of a memory opening fill structure according to a secondembodiment of the present disclosure.

FIG. 18 is a vertical cross-sectional view of a region of thealternative configuration of the second exemplary structure afterformation of backside contact via structures according to the secondembodiment of the present disclosure.

FIG. 19 is a band diagram of a region between an electrically conductivelayer and a vertical semiconductor channel within the second exemplarystructure of FIG. 16 when the external bias voltage to the electricallyconductive layer is zero.

DETAILED DESCRIPTION

As discussed above, the embodiments of the present disclosure aredirected to a three-dimensional memory device with composite chargestorage structures and methods of manufacturing the same, the variousaspects of which are described below. The embodiments of the disclosurecan be employed to form various structures including a multilevel memorystructure, non-limiting examples of which include semiconductor devicessuch as three-dimensional monolithic memory array devices comprising aplurality of NAND memory strings.

The drawings are not drawn to scale. Multiple instances of an elementmay be duplicated where a single instance of the element is illustrated,unless absence of duplication of elements is expressly described orclearly indicated otherwise. Ordinals such as “first,” “second,” and“third” are employed merely to identify similar elements, and differentordinals may be employed across the specification and the claims of theinstant disclosure. The term “at least one” element refers to allpossibilities including the possibility of a single element and thepossibility of multiple elements.

The same reference numerals refer to the same element or similarelement. Unless otherwise indicated, elements having the same referencenumerals are presumed to have the same composition and the samefunction. Unless otherwise indicated, a “contact” between elementsrefers to a direct contact between elements that provides an edge or asurface shared by the elements. If two or more elements are not indirect contact with each other or among one another, the two elementsare “disjoined from” each other or “disjoined among” one another. Asused herein, a first element located “on” a second element can belocated on the exterior side of a surface of the second element or onthe interior side of the second element. As used herein, a first elementis located “directly on” a second element if there exist a physicalcontact between a surface of the first element and a surface of thesecond element. As used herein, a first element is “electricallyconnected to” a second element if there exists a conductive pathconsisting of at least one conductive material between the first elementand the second element. As used herein, a “prototype” structure or an“in-process” structure refers to a transient structure that issubsequently modified in the shape or composition of at least onecomponent therein.

As used herein, a “layer” refers to a material portion including aregion having a thickness. A layer may extend over the entirety of anunderlying or overlying structure, or may have an extent less than theextent of an underlying or overlying structure. Further, a layer may bea region of a homogeneous or inhomogeneous continuous structure that hasa thickness less than the thickness of the continuous structure. Forexample, a layer may be located between any pair of horizontal planesbetween, or at, a top surface and a bottom surface of the continuousstructure. A layer may extend horizontally, vertically, and/or along atapered surface. A substrate may be a layer, may include one or morelayers therein, or may have one or more layer thereupon, thereabove,and/or therebelow.

As used herein, a first surface and a second surface are “verticallycoincident” with each other if the second surface overlies or underliesthe first surface and there exists a vertical plane or a substantiallyvertical plane that includes the first surface and the second surface. Asubstantially vertical plane is a plane that extends straight along adirection that deviates from a vertical direction by an angle less than5 degrees. A vertical plane or a substantially vertical plane isstraight along a vertical direction or a substantially verticaldirection, and may, or may not, include a curvature along a directionthat is perpendicular to the vertical direction or the substantiallyvertical direction.

A monolithic three-dimensional memory array is a memory array in whichmultiple memory levels are formed above a single substrate, such as asemiconductor wafer, with no intervening substrates. The term“monolithic” means that layers of each level of the array are directlydeposited on the layers of each underlying level of the array. Incontrast, two dimensional arrays may be formed separately and thenpackaged together to form a non-monolithic memory device. For example,non-monolithic stacked memories have been constructed by forming memorylevels on separate substrates and vertically stacking the memory levels,as described in U.S. Pat. No. 5,915,167 titled “Three-dimensionalStructure Memory.” The substrates may be thinned or removed from thememory levels before bonding, but as the memory levels are initiallyformed over separate substrates, such memories are not true monolithicthree-dimensional memory arrays. The various three-dimensional memorydevices of the present disclosure include a monolithic three-dimensionalNAND string memory device, and can be fabricated employing the variousembodiments described herein.

Referring to FIG. 1, a first exemplary structure according to a firstembodiment of the present disclosure is illustrated, which can beemployed, for example, to fabricate a device structure containingvertical NAND memory devices. The first exemplary structure includes asubstrate (9, 10), which can be a semiconductor substrate. The substratecan include a substrate semiconductor layer 9 and an optionalsemiconductor material layer 10. The substrate semiconductor layer 9 maybe a semiconductor wafer or a semiconductor material layer, and caninclude at least one elemental semiconductor material (e.g., singlecrystal silicon wafer or layer), at least one III-V compoundsemiconductor material, at least one II-VI compound semiconductormaterial, at least one organic semiconductor material, or othersemiconductor materials known in the art. The substrate can have a majorsurface 7, which can be, for example, a topmost surface of the substratesemiconductor layer 9. The major surface 7 can be a semiconductorsurface. In one embodiment, the major surface 7 can be a singlecrystalline semiconductor surface, such as a single crystallinesemiconductor surface.

As used herein, a “semiconducting material” refers to a material havingelectrical conductivity in the range from 1.0×10⁻⁵ S/m to 1.0×10⁵ S/m.As used herein, a “semiconductor material” refers to a material havingelectrical conductivity in the range from 1.0×10⁻⁵ S/m to 1.0 S/m in theabsence of electrical dopants therein, and is capable of producing adoped material having electrical conductivity in a range from 1.0 S/m to1.0×10⁵ S/m upon suitable doping with an electrical dopant. As usedherein, an “electrical dopant” refers to a p-type dopant that adds ahole to a valence band within a band structure, or an n-type dopant thatadds an electron to a conduction band within a band structure. As usedherein, a “conductive material” refers to a material having electricalconductivity greater than 1.0×10⁵ S/m. As used herein, an “insulatormaterial” or a “dielectric material” refers to a material havingelectrical conductivity less than 1.0×10⁻⁵ S/m. As used herein, a“heavily doped semiconductor material” refers to a semiconductormaterial that is doped with electrical dopant at a sufficiently highatomic concentration to become a conductive material either as formed asa crystalline material or if converted into a crystalline materialthrough an anneal process (for example, from an initial amorphousstate), i.e., to have electrical conductivity greater than 1.0×10⁵ S/m.A “doped semiconductor material” may be a heavily doped semiconductormaterial, or may be a semiconductor material that includes electricaldopants (i.e., p-type dopants and/or n-type dopants) at a concentrationthat provides electrical conductivity in the range from 1.0×10⁻⁵ S/m to1.0×10⁵ S/m. An “intrinsic semiconductor material” refers to asemiconductor material that is not doped with electrical dopants. Thus,a semiconductor material may be semiconducting or conductive, and may bean intrinsic semiconductor material or a doped semiconductor material. Adoped semiconductor material can be semiconducting or conductivedepending on the atomic concentration of electrical dopants therein. Asused herein, a “metallic material” refers to a conductive materialincluding at least one metallic element therein. All measurements forelectrical conductivities are made at the standard condition.

At least one semiconductor device 700 for a peripheral circuitry can beformed on a portion of the substrate semiconductor layer 9. The at leastone semiconductor device can include, for example, field effecttransistors. For example, at least one shallow trench isolationstructure 720 can be formed by etching portions of the substratesemiconductor layer 9 and depositing a dielectric material therein. Agate dielectric layer, at least one gate conductor layer, and a gate capdielectric layer can be formed over the substrate semiconductor layer 9,and can be subsequently patterned to form at least one gate structure(750, 752, 754, 758), each of which can include a gate dielectric 750, agate electrode (752, 754), and a gate cap dielectric 758. The gateelectrode (752, 754) may include a stack of a first gate electrodeportion 752 and a second gate electrode portion 754. At least one gatespacer 756 can be formed around the at least one gate structure (750,752, 754, 758) by depositing and anisotropically etching a dielectricliner. Active regions 730 can be formed in upper portions of thesubstrate semiconductor layer 9, for example, by introducing electricaldopants employing the at least one gate structure (750, 752, 754, 758)as masking structures. Additional masks may be employed as needed. Theactive region 730 can include source regions and drain regions of fieldeffect transistors. A first dielectric liner 761 and a second dielectricliner 762 can be optionally formed. Each of the first and seconddielectric liners (761, 762) can comprise a silicon oxide layer, asilicon nitride layer, and/or a dielectric metal oxide layer. As usedherein, silicon oxide includes silicon dioxide as well asnon-stoichiometric silicon oxides having more or less than two oxygenatoms for each silicon atoms. Silicon dioxide is preferred. In anillustrative example, the first dielectric liner 761 can be a siliconoxide layer, and the second dielectric liner 762 can be a siliconnitride layer. The least one semiconductor device for the peripheralcircuitry can contain a driver circuit for memory devices to besubsequently formed, which can include at least one NAND device.

A dielectric material such as silicon oxide can be deposited over the atleast one semiconductor device, and can be subsequently planarized toform a planarization dielectric layer 770. In one embodiment theplanarized top surface of the planarization dielectric layer 770 can becoplanar with a top surface of the dielectric liners (761, 762).Subsequently, the planarization dielectric layer 770 and the dielectricliners (761, 762) can be removed from an area to physically expose a topsurface of the substrate semiconductor layer 9. As used herein, asurface is “physically exposed” if the surface is in physical contactwith vacuum, or a gas phase material (such as air).

The optional semiconductor material layer 10, if present, can be formedon the top surface of the substrate semiconductor layer 9 prior to, orafter, formation of the at least one semiconductor device 700 bydeposition of a single crystalline semiconductor material, for example,by selective epitaxy. The deposited semiconductor material can be thesame as, or can be different from, the semiconductor material of thesubstrate semiconductor layer 9. The deposited semiconductor materialcan be any material that can be employed for the substrate semiconductorlayer 9 as described above. The single crystalline semiconductormaterial of the semiconductor material layer 10 can be in epitaxialalignment with the single crystalline structure of the substratesemiconductor layer 9. Portions of the deposited semiconductor materiallocated above the top surface of the planarization dielectric layer 770can be removed, for example, by chemical mechanical planarization (CMP).In this case, the semiconductor material layer 10 can have a top surfacethat is coplanar with the top surface of the planarization dielectriclayer 770.

The region (i.e., area) of the at least one semiconductor device 700 isherein referred to as a peripheral device region 200. The region inwhich a memory array is subsequently formed is herein referred to as amemory array region 100. A staircase region 300 for subsequently formingstepped terraces of electrically conductive layers can be providedbetween the memory array region 100 and the peripheral device region200.

Referring to FIG. 2, a stack of an alternating plurality of firstmaterial layers (which can be insulating layers 32) and second materiallayers (which can be sacrificial material layer 42) is formed over thetop surface of the substrate (9, 10). As used herein, a “material layer”refers to a layer including a material throughout the entirety thereof.As used herein, an alternating plurality of first elements and secondelements refers to a structure in which instances of the first elementsand instances of the second elements alternate. Each instance of thefirst elements that is not an end element of the alternating pluralityis adjoined by two instances of the second elements on both sides, andeach instance of the second elements that is not an end element of thealternating plurality is adjoined by two instances of the first elementson both ends. The first elements may have the same thicknessthereamongst, or may have different thicknesses. The second elements mayhave the same thickness thereamongst, or may have different thicknesses.The alternating plurality of first material layers and second materiallayers may begin with an instance of the first material layers or withan instance of the second material layers, and may end with an instanceof the first material layers or with an instance of the second materiallayers. In one embodiment, an instance of the first elements and aninstance of the second elements may form a unit that is repeated withperiodicity within the alternating plurality.

Each first material layer includes a first material, and each secondmaterial layer includes a second material that is different from thefirst material. In one embodiment, each first material layer can be aninsulating layer 32, and each second material layer can be a sacrificialmaterial layer. In this case, the stack can include an alternatingplurality of insulating layers 32 and sacrificial material layers 42,and constitutes a prototype stack of alternating layers comprisinginsulating layers 32 and sacrificial material layers 42.

The stack of the alternating plurality is herein referred to as analternating stack (32, 42). In one embodiment, the alternating stack(32, 42) can include insulating layers 32 composed of the firstmaterial, and sacrificial material layers 42 composed of a secondmaterial different from that of insulating layers 32. The first materialof the insulating layers 32 can be at least one insulating material. Assuch, each insulating layer 32 can be an insulating material layer.Insulating materials that can be employed for the insulating layers 32include, but are not limited to, silicon oxide (including doped orundoped silicate glass), silicon nitride, silicon oxynitride,organosilicate glass (OSG), spin-on dielectric materials, dielectricmetal oxides that are commonly known as high dielectric constant(high-k) dielectric oxides (e.g., aluminum oxide, hafnium oxide, etc.)and silicates thereof, dielectric metal oxynitrides and silicatesthereof, and organic insulating materials. In one embodiment, the firstmaterial of the insulating layers 32 can be silicon oxide.

The second material of the sacrificial material layers 42 is asacrificial material that can be removed selective to the first materialof the insulating layers 32. As used herein, a removal of a firstmaterial is “selective to” a second material if the removal processremoves the first material at a rate that is at least twice the rate ofremoval of the second material. The ratio of the rate of removal of thefirst material to the rate of removal of the second material is hereinreferred to as a “selectivity” of the removal process for the firstmaterial with respect to the second material. The sacrificial materiallayers 42 may comprise an insulating material, a semiconductor material,or a conductive material. The second material of the sacrificialmaterial layers 42 can be subsequently replaced with electricallyconductive electrodes which can function, for example, as control gateelectrodes of a vertical NAND device. Non-limiting examples of thesecond material include silicon nitride, an amorphous semiconductormaterial (such as amorphous silicon), and a polycrystallinesemiconductor material (such as polysilicon). In one embodiment, thesacrificial material layers 42 can be spacer material layers thatcomprise silicon nitride or a semiconductor material including at leastone of silicon and germanium.

In one embodiment, the insulating layers 32 can include silicon oxide,and sacrificial material layers can include silicon nitride sacrificialmaterial layers. The first material of the insulating layers 32 can bedeposited, for example, by chemical vapor deposition (CVD). For example,if silicon oxide is employed for the insulating layers 32, tetraethylorthosilicate (TEOS) can be employed as the precursor material for theCVD process. The second material of the sacrificial material layers 42can be formed, for example, CVD or atomic layer deposition (ALD). Thesacrificial material layers 42 can be suitably patterned so thatconductive material portions to be subsequently formed by replacement ofthe sacrificial material layers 42 can function as electricallyconductive electrodes, such as the control gate electrodes of themonolithic three-dimensional NAND string memory devices to besubsequently formed. The sacrificial material layers 42 may comprise aportion having a strip shape extending substantially parallel to themajor surface 7 of the substrate.

The thicknesses of the insulating layers 32 and the sacrificial materiallayers 42 can be in a range from 20 nm to 50 nm, although lesser andgreater thicknesses can be employed for each insulating layer 32 and foreach sacrificial material layer 42. The number of repetitions of thepairs of an insulating layer 32 and a sacrificial material layer (e.g.,a control gate electrode or a sacrificial material layer) 42 can be in arange from 2 to 1,024, and typically from 8 to 256, although a greaternumber of repetitions can also be employed. The top and bottom gateelectrodes in the stack may function as the select gate electrodes. Inone embodiment, each sacrificial material layer 42 in the alternatingstack (32, 42) can have a uniform thickness that is substantiallyinvariant within each respective sacrificial material layer 42.

While the present disclosure is described employing an embodiment inwhich the spacer material layers are sacrificial material layers 42 thatare subsequently replaced with electrically conductive layers,embodiments are expressly contemplated herein in which the sacrificialmaterial layers are formed as electrically conductive layers. In thiscase, steps for replacing the spacer material layers with electricallyconductive layers can be omitted.

The topmost layer of the alternating stack (32, 42) can be an insulatinglayer, which is herein referred to as a topmost insulating layer 32T,which can be formed over the alternating stack (32, 42). The topmostinsulating layer 32T can have a greater thickness than each of theinsulating layers 32. The topmost insulating layer 32T can be deposited,for example, by chemical vapor deposition. In one embodiment, thetopmost insulating layer 32T can be a silicon oxide layer.

Referring to FIG. 3, stepped surfaces are formed at a peripheral regionof the alternating stack (32, 42), which is herein referred to as aterrace region. As used herein, “stepped surfaces” refer to a set ofsurfaces that include at least two horizontal surfaces and at least twovertical surfaces such that each horizontal surface is adjoined to afirst vertical surface that extends upward from a first edge of thehorizontal surface, and is adjoined to a second vertical surface thatextends downward from a second edge of the horizontal surface. A steppedcavity is formed within the volume from which portions of thealternating stack (32, 42) are removed through formation of the steppedsurfaces. A “stepped cavity” refers to a cavity having stepped surfaces.

The terrace region is formed in the staircase region 300, which islocated between the memory array region 100 and the peripheral deviceregion 200 containing the at least one semiconductor device for theperipheral circuitry. The stepped cavity can have various steppedsurfaces such that the horizontal cross-sectional shape of the steppedcavity changes in steps as a function of the vertical distance from thetop surface of the substrate (9, 10). In one embodiment, the steppedcavity can be formed by repetitively performing a set of processingsteps. The set of processing steps can include, for example, an etchprocess of a first type that vertically increases the depth of a cavityby one or more levels, and an etch process of a second type thatlaterally expands the area to be vertically etched in a subsequent etchprocess of the first type. As used herein, a “level” of a structureincluding alternating plurality is defined as the relative position of apair of a first material layer and a second material layer within thestructure.

Each sacrificial material layer 42 other than a topmost sacrificialmaterial layer 42 within the alternating stack (32, 42) laterallyextends farther than any overlying sacrificial material layer 42 withinthe alternating stack (32, 42) in the terrace region. The terrace regionincludes stepped surfaces of the alternating stack (32, 42) thatcontinuously extend from a bottommost layer within the alternating stack(32, 42) to a topmost layer within the alternating stack (32, 42).

Each vertical step of the stepped surfaces can have the height of one ormore pairs of an insulating layer 32 and a sacrificial material layer.In one embodiment, each vertical step can have the height of a singlepair of an insulating layer 32 and a sacrificial material layer 42. Inanother embodiment, multiple “columns” of staircases can be formed alonga first horizontal direction hd1 such that each vertical step has theheight of a plurality of pairs of an insulating layer 32 and asacrificial material layer 42, and the number of columns can be at leastthe number of the plurality of pairs. Each column of staircase can bevertically offset among one another such that each of the sacrificialmaterial layers 42 has a physically exposed top surface in a respectivecolumn of staircases. In the illustrative example, two columns ofstaircases are formed for each block of memory stack structures to besubsequently formed such that one column of staircases providephysically exposed top surfaces for odd-numbered sacrificial materiallayers 42 (as counted from the bottom) and another column of staircasesprovide physically exposed top surfaces for even-numbered sacrificialmaterial layers (as counted from the bottom). Configurations employingthree, four, or more columns of staircases with a respective set ofvertical offsets among the physically exposed surfaces of thesacrificial material layers 42 may also be employed. Each sacrificialmaterial layer 42 has a greater lateral extent, at least along onedirection, than any overlying sacrificial material layers 42 such thateach physically exposed surface of any sacrificial material layer 42does not have an overhang. In one embodiment, the vertical steps withineach column of staircases may be arranged along the first horizontaldirection hd1, and the columns of staircases may be arranged along asecond horizontal direction hd2 that is perpendicular to the firsthorizontal direction hd1. In one embodiment, the first horizontaldirection hd1 may be perpendicular to the boundary between the memoryarray region 100 and the staircase region 300.

A retro-stepped dielectric material portion 65 (i.e., an insulating fillmaterial portion) can be formed in the stepped cavity by deposition of adielectric material therein. For example, a dielectric material such assilicon oxide can be deposited in the stepped cavity. Excess portions ofthe deposited dielectric material can be removed from above the topsurface of the topmost insulating layer 32T, for example, by chemicalmechanical planarization (CMP). The remaining portion of the depositeddielectric material filling the stepped cavity constitutes theretro-stepped dielectric material portion 65. As used herein, a“retro-stepped” element refers to an element that has stepped surfacesand a horizontal cross-sectional area that increases monotonically as afunction of a vertical distance from a top surface of a substrate onwhich the element is present. If silicon oxide is employed for theretro-stepped dielectric material portion 65, the silicon oxide of theretro-stepped dielectric material portion 65 may, or may not, be dopedwith dopants such as B, P, and/or F.

Optionally, drain select level isolation structures 72 can be formedthrough the topmost insulating layer 32T and a subset of the sacrificialmaterial layers 42 located at drain select levels. The drain selectlevel isolation structures 72 can be formed, for example, by formingdrain select level isolation trenches and filling the drain select levelisolation trenches with a dielectric material such as silicon oxide.Excess portions of the dielectric material can be removed from above thetop surface of the topmost insulating layer 32T.

Referring to FIGS. 4A and 4B, a lithographic material stack (not shown)including at least a photoresist layer can be formed over the topmostinsulating layer 32T and the retro-stepped dielectric material portion65, and can be lithographically patterned to form openings therein. Theopenings include a first set of openings formed over the memory arrayregion 100 and a second set of openings formed over the staircase region300. The pattern in the lithographic material stack can be transferredthrough the topmost insulating layer 32T or the retro-stepped dielectricmaterial portion 65, and through the alternating stack (32, 42) by atleast one anisotropic etch that employs the patterned lithographicmaterial stack as an etch mask. Portions of the alternating stack (32,42) underlying the openings in the patterned lithographic material stackare etched to form memory openings 49 and support openings 19. As usedherein, a “memory opening” refers to a structure in which memoryelements, such as a memory stack structure, is subsequently formed. Asused herein, a “support opening” refers to a structure in which asupport structure (such as a support pillar structure) that mechanicallysupports other elements is subsequently formed. The memory openings 49are formed through the topmost insulating layer 32T and the entirety ofthe alternating stack (32, 42) in the memory array region 100. Thesupport openings 19 are formed through the retro-stepped dielectricmaterial portion 65 and the portion of the alternating stack (32, 42)that underlie the stepped surfaces in the staircase region 300.

The memory openings 49 extend through the entirety of the alternatingstack (32, 42). The support openings 19 extend through a subset oflayers within the alternating stack (32, 42). The chemistry of theanisotropic etch process employed to etch through the materials of thealternating stack (32, 42) can alternate to optimize etching of thefirst and second materials in the alternating stack (32, 42). Theanisotropic etch can be, for example, a series of reactive ion etches.The sidewalls of the memory openings 49 and the support openings 19 canbe substantially vertical, or can be tapered. The patterned lithographicmaterial stack can be subsequently removed, for example, by ashing.

The memory openings 49 and the support openings 19 can extend from thetop surface of the alternating stack (32, 42) to at least the horizontalplane including the topmost surface of the semiconductor material layer10. In one embodiment, an overetch into the semiconductor material layer10 may be optionally performed after the top surface of thesemiconductor material layer 10 is physically exposed at a bottom ofeach memory opening 49 and each support opening 19. The overetch may beperformed prior to, or after, removal of the lithographic materialstack. In other words, the recessed surfaces of the semiconductormaterial layer 10 may be vertically offset from the un-recessed topsurfaces of the semiconductor material layer 10 by a recess depth. Therecess depth can be, for example, in a range from 1 nm to 50 nm,although lesser and greater recess depths can also be employed. Theoveretch is optional, and may be omitted. If the overetch is notperformed, the bottom surfaces of the memory openings 49 and the supportopenings 19 can be coplanar with the topmost surface of thesemiconductor material layer 10.

Each of the memory openings 49 and the support openings 19 may include asidewall (or a plurality of sidewalls) that extends substantiallyperpendicular to the topmost surface of the substrate. A two-dimensionalarray of memory openings 49 can be formed in the memory array region100. A two-dimensional array of support openings 19 can be formed in thestaircase region 300. The substrate semiconductor layer 9 and thesemiconductor material layer 10 collectively constitutes a substrate (9,10), which can be a semiconductor substrate. Alternatively, thesemiconductor material layer 10 may be omitted, and the memory openings49 and the support openings 19 can be extend to a top surface of thesubstrate semiconductor layer 9.

FIGS. 5A-5H illustrate structural changes in a memory opening 49, whichis one of the memory openings 49 in the first exemplary structure ofFIGS. 4A and 4B. The same structural change occurs simultaneously ineach of the other memory openings 49 and in each of the support openings19.

Referring to FIG. 5A, a memory opening 49 in the exemplary devicestructure of FIGS. 4A and 4B is illustrated. The memory opening 49extends through the topmost insulating layer 32T, the alternating stack(32, 42), and optionally into an upper portion of the semiconductormaterial layer 10. At this processing step, each support opening 19 canextend through the retro-stepped dielectric material portion 65, asubset of layers in the alternating stack (32, 42), and optionallythrough the upper portion of the semiconductor material layer 10. Therecess depth of the bottom surface of each memory opening with respectto the top surface of the semiconductor material layer 10 can be in arange from 0 nm to 30 nm, although greater recess depths can also beemployed. Optionally, the sacrificial material layers 42 can belaterally recessed partially to form lateral recesses (not shown), forexample, by an isotropic etch.

Referring to FIG. 5B, an optional pedestal channel portion (e.g., anepitaxial pedestal) 11 can be formed at the bottom portion of eachmemory opening 49 and each support openings 19, for example, byselective epitaxy. Each pedestal channel portion 11 comprises a singlecrystalline semiconductor material in epitaxial alignment with thesingle crystalline semiconductor material of the semiconductor materiallayer 10. In one embodiment, the top surface of each pedestal channelportion 11 can be formed above a horizontal plane including the topsurface of a bottommost sacrificial material layer 42. In this case, asource select gate electrode can be subsequently formed by replacing thebottommost sacrificial material layer 42 with a conductive materiallayer. The pedestal channel portion 11 can be a portion of a transistorchannel that extends between a source region to be subsequently formedin the substrate (9, 10) and a drain region to be subsequently formed inan upper portion of the memory opening 49. A memory cavity 49′ ispresent in the unfilled portion of the memory opening 49 above thepedestal channel portion 11. In one embodiment, the pedestal channelportion 11 can comprise single crystalline silicon. In one embodiment,the pedestal channel portion 11 can have a doping of the firstconductivity type, which is the same as the conductivity type of thesemiconductor material layer 10 that the pedestal channel portioncontacts. If a semiconductor material layer 10 is not present, thepedestal channel portion 11 can be formed directly on the substratesemiconductor layer 9, which can have a doping of the first conductivitytype.

Referring to FIG. 5C, the spacer material layers (such as thesacrificial material layers 42) are laterally recessed selective to theinsulating layers 32 by a first isotropic etch process to form annularrecess regions 349. The first isotropic etch process can laterallyrecess sidewalls of the spacer material layers (such as the sacrificialmaterial layers 42) relative to sidewalls of the insulating layers 32around each memory opening 49. In one embodiment, the first isotropicetch process may include a wet etch process. For example, if theinsulating layers 32 include a silicon oxide material and if thesacrificial material layers 42 include silicon nitride, a wet etchprocess employing hot phosphoric acid can be employed to selectivelyetch the material of the sacrificial material layers 42 selective to thematerial of the insulating layers 32. The lateral recess distance of thefirst isotropic etch process can be in a range from 10 nm to 100 nm,such as from 20 nm to 50 nm, although lesser and greater lateral recessdistances can also be employed.

Referring to FIG. 5D, the insulating layers 32 can optionally beisotropically recessed selective to the spacer material layers (such asthe sacrificial material layers 42) by a second isotropic etch process.Surfaces of the insulating layers 32 are isotropically trimmed to formannular grooves that are laterally bounded by a concave surface of arespective insulating layer 32 and vertically bounded by a horizontalsurface of a respective spacer material layer (such as a sacrificialmaterial layer 42). The second isotropic etch process can isotropicallyrecess sidewalls of the insulating layers 32 selective to the materialspacer material layers (such as the sacrificial material layers 42)around each memory opening 49. In one embodiment, the second isotropicetch process may include a wet etch process. For example, if theinsulating layers 32 include a silicon oxide material and if thesacrificial material layers 42 include silicon nitride, a wet etchprocess employing dilute hydrofluoric acid can be employed toselectively etch the material of the insulating layers 32 selective tothe material of the sacrificial material layers 42. The lateral recessdistance of the second isotropic etch process can be less than one halfof the vertical thickness of the insulating layers 32, and can be in arange from 2 nm to 12 nm, such as from 3 nm to 8 nm, although lesser andgreater lateral recess distances can also be employed. Annular topsurfaces of the sacrificial material layers 42 and annular bottomsurfaces of the sacrificial material layers 42 can be physically exposedto the annular recess regions. A pair of annular grooves can be adjoinedto each annular recess region 349.

Referring to FIG. 5E, a blocking dielectric layer 52 can be conformallydeposited on physically exposed surfaces of the insulating layers 32 andthe spacer material layers (such as the sacrificial material layers 42).The blocking dielectric layer 52 includes at least one dielectricmaterial, and may include a single dielectric material layer or a stackof a plurality of dielectric material layers. The blocking dielectriclayer 52 can have a total thickness that is the same as, greater than,or less than, the isotropic recess distance of the second isotropic etchprocess of step 5D. In one embodiment, the blocking dielectric layer 52can include a dielectric metal oxide layer consisting essentially of adielectric metal oxide. As used herein, a dielectric metal oxide refersto a dielectric material that includes at least one metallic element andat least oxygen. The dielectric metal oxide may consist essentially ofthe at least one metallic element and oxygen, or may consist essentiallyof the at least one metallic element, oxygen, and at least onenon-metallic element such as nitrogen. In one embodiment, the blockingdielectric layer 52 can include a dielectric metal oxide having adielectric constant greater than 7.9, i.e., having a dielectric constantgreater than the dielectric constant of silicon nitride.

Non-limiting examples of dielectric metal oxides include aluminum oxide(Al₂O₃), hafnium oxide (HfO₂), lanthanum oxide (LaO₂), yttrium oxide(Y₂O₃), tantalum oxide (Ta₂O₅), silicates thereof, nitrogen-dopedcompounds thereof, alloys thereof, and stacks thereof. The dielectricmetal oxide layer can be deposited, for example, by chemical vapordeposition (CVD), atomic layer deposition (ALD), pulsed laser deposition(PLD), liquid source misted chemical deposition, or a combinationthereof. The thickness of the dielectric metal oxide layer can be in arange from 1 nm to 20 nm, although lesser and greater thicknesses canalso be employed. The dielectric metal oxide layer can subsequentlyfunction as a dielectric material portion that blocks leakage of storedelectrical charges to control gate electrodes. In one embodiment, theblocking dielectric layer 52 includes aluminum oxide. In one embodiment,the blocking dielectric layer 52 can include multiple dielectric metaloxide layers having different material compositions.

Alternatively or additionally, the blocking dielectric layer 52 caninclude a dielectric semiconductor compound such as silicon oxide,silicon oxynitride, silicon nitride, or a combination thereof. In oneembodiment, the blocking dielectric layer 52 can include silicon oxide.In this case, the dielectric semiconductor compound of the blockingdielectric layer 52 can be formed by a conformal deposition method suchas low pressure chemical vapor deposition, atomic layer deposition, or acombination thereof. The thickness of the dielectric semiconductorcompound can be in a range from 1 nm to 20 nm, such as from 2 nm to 6nm, although lesser and greater thicknesses can also be employed.Alternatively, the blocking dielectric layer 52 can be omitted, and abackside blocking dielectric layer can be formed after formation ofbackside recesses on surfaces of memory films to be subsequently formed.

The blocking dielectric layer 52 continuously extends through levels ofa plurality of insulating layers 32 and a plurality of sacrificialmaterial layers 42 within the alternating stack (32, 42). The blockingdielectric layer 52 has a laterally undulating vertical cross-sectionalprofile that conforms to the vertical cross-sectional profile of thealternating stack (32, 42) of the insulating layers 32 and thesacrificial material layers 42. Thus, the blocking dielectric layer 52comprises laterally-protruding portions that protrude outward at eachlevel of the annular recess regions 349 (and therefore, at each level ofthe sacrificial material layers 42). Further, a pair of annular ridgescan laterally protrude from each laterally-protruding portion of theblocking dielectric layer 52 around each memory opening 49.

The interfaces between the blocking dielectric layer 52 and theinsulating layers 32 can include annular horizontal surface portions andannular curved surface portions. A concave annular surface segment of aninsulating layer 32 contacts a convex annular surface segment of theblocking dielectric layer 52 at each annular curved surface portion ofthe interfaces between the blocking dielectric layer 52 and theinsulating layers 32. The annular horizontal surface portions of theinterfaces can be vertically offset from interfaces between theinsulating layers 32 and the sacrificial material layers 42.

In one embodiment, an inner sidewall of the blocking dielectric layer 52comprises insulating-layer-level sidewall segments located at levels ofthe insulating layers 32, and annular recessed sidewall segments thatare located at levels of the plurality of sacrificial material layers 42and laterally recessed outward relative to insulating-layer-levelsidewall segments.

Referring to FIG. 5F, a first charge trapping material can beconformally deposited in unfilled volumes of the annular recess regions349 by a conformal deposition process. A conformal charge trappingmaterial layer 53L including the first charge trapping material can beformed. According to an aspect of the present disclosure, the conformalcharge trapping material layer 53L includes a charge trapping materialhaving a higher charge trap density than a charge storage layer to besubsequently deposited. In one embodiment, the conformal charge trappingmaterial layer 53L can include a charge trapping dielectric materialhaving a greater charge trap density and greater electronmovement/diffusion than stoichiometric silicon nitride. For example, theconformal charge trapping material layer 53L can include aluminumnitride. The conformal charge trapping material layer 53L can bedeposited by a conformal deposition process such as a chemicalmechanical deposition process or an atomic layer deposition process. Thethickness of the conformal charge trapping material layer 53L can begreater than the recess distance of the recessed portions of thephysically exposed sidewall of the blocking dielectric layer 52 atlevels of the sacrificial material layers 42 relative to the unrecessedportions of the physically exposed sidewall of the blocking dielectriclayer 52 at levels of the insulating layers 32. For example, thethickness of the conformal charge trapping material layer 53L can be ina range from 3 nm to 40 nm, such as from 6 nm to 20 nm, although lesserand greater thicknesses can also be employed.

Referring to FIG. 5G, an anisotropic etch process that etches thematerial of the conformal charge trapping material layer 53L selectiveto the material of the blocking dielectric layer 52. The anisotropicetch process etches unmasked portions of the first charge trappingmaterial. Portions of the conformal charge trapping material layer 53Lthat do not underlie an overlying portion of the blocking dielectriclayer 52 are removed by the anisotropic etch process. Specifically,portions of the first charge trapping material located inside acylindrical volume defined by inner sidewall segments of the blockingdielectric layer 52 located at levels of the insulating layers 32 can beremoved by the anisotropic etch process. The remaining portions of thefirst charge trapping material comprise tubular charge storage materialportions 53.

A vertical stack of tubular charge storage material portions 53 can beformed within each memory opening 49. Each tubular charge storagematerial portion 53 includes the first charge trapping material. Thetubular charge storage material portions 53 can be located at levels ofthe sacrificial material layers 42 as discrete material portions thatare vertically spaced apart by the insulating layers 32. Each tubularcharge storage material portion 53 can have a respective tubular shapewith a uniform lateral distance between an inner cylindrical sidewalland an outer cylindrical sidewall. Each tubular charge storage materialportion 53 can have a planar annular top surface and a planar annularbottom surface.

Each of the tubular charge storage material portions 53 can be formedwithin volumes of the annular recess regions 349. The tubular chargestorage material portions 53 are formed on the blocking dielectric layer52. The tubular charge storage material portions 53 can include aluminumnitride.

Referring to FIG. 5H, a continuous charge storage layer 54 including asecond charge storage material can be formed by a conformal depositionprocess. The charge storage layer 54 can be formed as a single chargestorage material layer having a homogeneous composition. The secondcharge storage material can have a lower charge trap density and lowerelectron movement/diffusion than the first charge storage material. Inone embodiment, the charge storage layer 54 includes stoichiometricsilicon nitride, i.e., a silicon nitride material having a materialcomposition of Si₃N₄. The charge storage layer 54 can be formed as asingle continuous layer. The thickness of the charge storage layer 54can be in a range from 2 nm to 20 nm, such as from 3 nm to 8 nm,although lesser and greater thicknesses can also be employed.

The lower charge trap density of the second charge storage material isadvantageous for preventing diffusion of electrical charge (e.g.,electrons) from levels of the sacrificial material layers 42 (which aresubsequently replaced with electrically conductive layers) to the levelof an overlying insulating layer 32 or to the level of an underlyinginsulating layer 32. The higher charge trap density of the first chargestorage material is advantageous for storing more electrical charge(e.g., electrons) during operation of a three-dimensional memory deviceemploying the combination of a vertical stack of discrete (e.g.,vertically separated) tubular charge storage material portions 53 andthe continuous charge storage layer 54 as a composite charge storagestructure (53, 54).

A tunneling dielectric layer 56 can be deposited over the charge storagelayer 54. The tunneling dielectric layer 56 includes a dielectricmaterial through which charge tunneling can be performed under suitableelectrical bias conditions. The charge tunneling may be performedthrough hot-carrier injection or by Fowler-Nordheim tunneling inducedcharge transfer depending on the mode of operation of the monolithicthree-dimensional NAND string memory device to be formed. The tunnelingdielectric layer 56 can include silicon oxide, silicon nitride, siliconoxynitride, dielectric metal oxides (such as aluminum oxide and hafniumoxide), dielectric metal oxynitride, dielectric metal silicates, alloysthereof, and/or combinations thereof. In one embodiment, the tunnelingdielectric layer 56 can include a stack of a first silicon oxide layer,a silicon oxynitride layer, and a second silicon oxide layer, which iscommonly known as an ONO stack. In one embodiment, the tunnelingdielectric layer 56 can include a silicon oxide layer that issubstantially free of carbon or a silicon oxynitride layer that issubstantially free of carbon. The thickness of the tunneling dielectriclayer 56 can be in a range from 2 nm to 20 nm, although lesser andgreater thicknesses can also be employed.

An optional first semiconductor channel layer 601 can be formed on thetunneling dielectric layer 56. The optional first semiconductor channellayer 601 includes a semiconductor material such as at least oneelemental semiconductor material, at least one III-V compoundsemiconductor material, at least one II-VI compound semiconductormaterial, at least one organic semiconductor material, or othersemiconductor materials known in the art. In one embodiment, the firstsemiconductor channel layer 601 includes amorphous silicon orpolysilicon. The first semiconductor channel layer 601 can be formed bya conformal deposition method such as low pressure chemical vapordeposition (LPCVD). The thickness of the first semiconductor channellayer 601 can be in a range from 2 nm to 10 nm, although lesser andgreater thicknesses can also be employed. A memory cavity 49′ is formedin the volume of each memory opening 49 that is not filled with thedeposited material portions (52, 53, 54, 56, 601).

Referring to FIG. 5I, the optional first semiconductor channel layer601, the tunneling dielectric layer 56, the charge storage layer 54, andthe blocking dielectric layer 52 are sequentially anisotropically etchedemploying at least one anisotropic etch process. The portions of thefirst semiconductor channel layer 601, the tunneling dielectric layer56, the charge storage layer 54, and the blocking dielectric layer 52located above the top surface of the topmost insulating layer 32T can beremoved by the at least one anisotropic etch process. Further, thehorizontal portions of the first semiconductor channel layer 601, thetunneling dielectric layer 56, the charge storage layer 54, and theblocking dielectric layer 52 at a bottom of each memory cavity 49′ canbe removed to form openings in remaining portions thereof. Each of thefirst semiconductor channel layer 601, the tunneling dielectric layer56, the charge storage layer 54, and the blocking dielectric layer 52can be etched by a respective anisotropic etch process employing arespective etch chemistry, which may, or may not, be the same for thevarious material layers. Each remaining portion of the firstsemiconductor channel layer 601 can have a tubular configuration.

A surface of the pedestal channel portion 11 (or a surface of thesemiconductor material layer 10 in case the pedestal channel portions 11are not employed) can be physically exposed underneath the openingthrough the first semiconductor channel layer 601, the tunnelingdielectric layer 56, the charge storage layer 54, and the blockingdielectric layer 52. Optionally, the physically exposed semiconductorsurface at the bottom of each memory cavity 49′ can be verticallyrecessed so that the recessed semiconductor surface underneath thememory cavity 49′ is vertically offset from the topmost surface of thepedestal channel portion 11 (or of the semiconductor material layer 10in case pedestal channel portions 11 are not employed) by a recessdistance. A tunneling dielectric layer 56 is located over the chargestorage layer 54. A set of a blocking dielectric layer 52, a verticalstack of tubular charge storage material portions 53, a charge storagelayer 54, and a tunneling dielectric layer 56 in a memory opening 49constitutes a memory film 50. The combination of the vertical stack oftubular charge storage material portions 53 and the charge storage layer54 constitutes a composite charge storage structure (53, 54). Thecomposite charge storage structure (53, 54) includes a plurality ofcharge storage regions that are insulated from surrounding materials bythe blocking dielectric layer 52 and the tunneling dielectric layer 56.Each charge storage region can include a respective tubular chargestorage material portion 53 and an adjoining portions of the chargestorage layer 54 located at a respective level of a sacrificial materiallayer 42. In one embodiment, the first semiconductor channel layer 601,the tunneling dielectric layer 56, the charge storage layer 54, and theblocking dielectric layer 52 can have vertically coincident sidewalls.

Referring to FIG. 5J, a second semiconductor channel layer 602 can bedeposited directly on the semiconductor surface of the pedestal channelportion 11 or the semiconductor material layer 10 if the pedestalchannel portion 11 is omitted, and directly on the first semiconductorchannel layer 601. The second semiconductor channel layer 602 includes asemiconductor material such as at least one elemental semiconductormaterial, at least one III-V compound semiconductor material, at leastone II-VI compound semiconductor material, at least one organicsemiconductor material, or other semiconductor materials known in theart. In one embodiment, the second semiconductor channel layer 602includes amorphous silicon or polysilicon. The second semiconductorchannel layer 602 can be formed by a conformal deposition method such aslow pressure chemical vapor deposition (LPCVD). The thickness of thesecond semiconductor channel layer 602 can be in a range from 2 nm to 10nm, although lesser and greater thicknesses can also be employed. Thesecond semiconductor channel layer 602 may partially fill the memorycavity 49′ in each memory opening, or may fully fill the cavity in eachmemory opening.

The materials of the first semiconductor channel layer 601 and thesecond semiconductor channel layer 602 are collectively referred to as asemiconductor channel material. In other words, the semiconductorchannel material is a set of all semiconductor material in the firstsemiconductor channel layer 601 and the second semiconductor channellayer 602.

Referring to FIG. 5K, in case the memory cavity 49′ in each memoryopening is not completely filled by the second semiconductor channellayer 602, a dielectric core layer 62L can be deposited in the memorycavity 49′ to fill any remaining portion of the memory cavity 49′ withineach memory opening. The dielectric core layer 62L includes a dielectricmaterial such as silicon oxide or organosilicate glass. The dielectriccore layer 62L can be deposited by a conformal deposition method such aslow pressure chemical vapor deposition (LPCVD), or by a self-planarizingdeposition process such as spin coating.

Referring to FIG. 5L, the horizontal portion of the dielectric corelayer 62L can be removed, for example, by a recess etch from above thetop surface of the second semiconductor channel layer 602. Further, thematerial of the dielectric core layer 62L can be vertically recessedselective to the semiconductor material of the second semiconductorchannel layer 602 into each memory opening 49 down to a depth between afirst horizontal plane including the top surface of the topmostinsulating layer 32T and a second horizontal plane including the bottomsurface of the topmost insulating layer 32T. Each remaining portion ofthe dielectric core layer 62L constitutes a dielectric core 62.

Referring to FIG. 5M, a doped semiconductor material having a doping ofa second conductivity type can be deposited within each recessed regionabove the dielectric cores 62. The second conductivity type is theopposite of the first conductivity type. For example, if the firstconductivity type is p-type, the second conductivity type is n-type, andvice versa. The dopant concentration of the doped semiconductor materialcan be in a range from 5.0×10′⁸/cm³ to 2.0×10²¹/cm³, although lesser andgreater dopant concentrations can also be employed. The dopedsemiconductor material can be, for example, doped polysilicon.

Excess portions of the deposited semiconductor material can be removedfrom above the top surface of the topmost insulating layer 32T, forexample, by chemical mechanical planarization (CMP) or a recess etch.Each remaining portion of the semiconductor material having a doping ofthe second conductively type constitutes a drain region 63. Thehorizontal portion of the second semiconductor channel layer 602 locatedabove the top surface of the topmost insulating layer 32T can beconcurrently removed by a planarization process. Each remaining portionof the second semiconductor channel layer 602 can be located entiretywithin a memory opening 49 or entirely within a support opening 19.

Each remaining portion of the doped semiconductor material having adoping of the second conductivity type constitutes a drain region 63.Each adjoining pair of a first semiconductor channel layer 601 and asecond semiconductor channel layer 602 can collectively form a verticalsemiconductor channel 60 through which electrical current can flow whena vertical NAND device including the vertical semiconductor channel 60is turned on. A tunneling dielectric layer 56 is surrounded by a chargestorage layer 54, and laterally surrounds a portion of the verticalsemiconductor channel 60. Each adjoining set of a tunneling dielectriclayer 56, a vertical stack of tubular charge storage material portions53, a charge storage layer 54, and a blocking dielectric layer 52collectively constitute a memory film 50, which includes a verticalstack of memory elements that can store a respective data bit with amacroscopic retention time. As used herein, a macroscopic retention timerefers to a retention time suitable for operation of a memory device asa permanent memory device such as a retention time in excess of 24hours. In alternative embodiments, a blocking dielectric layer 52 maynot be formed in each memory opening 49, and may be subsequently formedin backside recesses that are formed by removal of the sacrificialmaterial layers 42 at a subsequent processing step.

Each combination of a memory film 50 and a vertical semiconductorchannel 60 within a memory opening 49 constitutes a memory stackstructure 55. The memory stack structure 55 is a combination of avertical semiconductor channel 60, a tunneling dielectric layer 56, aplurality of memory elements comprising tubular charge storage materialportions 53 and portions of the charge storage layer 54 contacting arespective one of the tubular charge storage material portions 53, and ablocking dielectric layer 52. Each combination of a pedestal channelportion 11 (if present), a memory stack structure 55, a dielectric core62, and a drain region 63 within a memory opening 49 is herein referredto as a memory opening fill structure 58. Each combination of a pedestalchannel portion 11 (if present), a memory film 50, a verticalsemiconductor channel 60, a dielectric core 62, and a drain region 63within each support opening 19 fills the respective support openings 19,and constitutes a support pillar structure.

Referring to FIG. 6, the first exemplary structure is illustrated afterformation of memory opening fill structures 58 and support pillarstructure 20 within the memory openings 49 and the support openings 19,respectively. An instance of a memory opening fill structure 58 can beformed within each memory opening 49 of the structure of FIGS. 4A and4B. An instance of the support pillar structure 20 can be formed withineach support opening 19 of the structure of FIGS. 4A and 4B.

Each memory stack structure 55 includes a vertical semiconductor channel60, which may comprise multiple semiconductor channel layers (601, 602),and a memory film 50. The memory film 50 may comprise a tunnelingdielectric layer 56 laterally surrounding the vertical semiconductorchannel 60, a vertical stack of charge storage elements (comprising atubular charge storage material portion 53 and an adjoined portion of acharge storage layer 54) laterally surrounding the tunneling dielectriclayer 56, and an optional blocking dielectric layer 52. While thepresent disclosure is described employing the illustrated configurationfor the memory stack structure, the methods of the present disclosurecan be applied to alternative memory stack structures includingdifferent layer stacks or structures for the memory film 50 and/or forthe vertical semiconductor channel 60.

Referring to FIGS. 7A-7C, a contact-level dielectric layer 73 can beformed over the alternating stack (32, 42) of insulating layer 32 andsacrificial material layers 42, and over the memory stack structures 55and the support pillar structures 20. The contact-level dielectric layer73 includes a dielectric material that is different from the dielectricmaterial of the sacrificial material layers 42. For example, thecontact-level dielectric layer 73 can include silicon oxide. Thecontact-level dielectric layer 73 can have a thickness in a range from50 nm to 500 nm, although lesser and greater thicknesses can also beemployed.

A photoresist layer (not shown) can be applied over the contact-leveldielectric layer 73, and is lithographically patterned to form openingsin areas between clusters of memory stack structures 55. The pattern inthe photoresist layer can be transferred through the contact-leveldielectric layer 73, the alternating stack (32, 42) and/or theretro-stepped dielectric material portion 65 employing an anisotropicetch to form backside trenches 79, which vertically extend from the topsurface of the contact-level dielectric layer 73 at least to the topsurface of the substrate (9, 10), and laterally extend through thememory array region 100 and the staircase region 300.

In one embodiment, the backside trenches 79 can laterally extend along afirst horizontal direction hd1 and can be laterally spaced apart fromeach other along a second horizontal direction hd2 that is perpendicularto the first horizontal direction hd1. The memory stack structures 55can be arranged in rows that extend along the first horizontal directionhd1. The drain select level isolation structures 72 can laterally extendalong the first horizontal direction hd1. Each backside trench 79 canhave a uniform width that is invariant along the lengthwise direction(i.e., along the first horizontal direction hd1). Each drain selectlevel isolation structure 72 can have a uniform vertical cross-sectionalprofile along vertical planes that are perpendicular to the firsthorizontal direction hd1 that is invariant with translation along thefirst horizontal direction hd1. Multiple rows of memory stack structures55 can be located between a neighboring pair of a backside trench 79 anda drain select level isolation structure 72, or between a neighboringpair of drain select level isolation structures 72. In one embodiment,the backside trenches 79 can include a source contact opening in which asource contact via structure can be subsequently formed. The photoresistlayer can be removed, for example, by ashing.

Referring to FIG. 8, dopants of the second conductivity type can beimplanted into portions of the semiconductor material layer 10 thatunderlie the backside trenches 79 to form source regions 61. The atomicconcentration of the dopants of the second conductivity type in thesource regions 61 can be in a range from 5.0×10¹⁹/cm³ to 2.0×10²¹/cm³,although lesser and greater atomic concentrations can also be employed.Surface portions of the semiconductor material layer 10 that extendbetween each source region 61 and adjacent memory opening fillstructures 58 comprise horizontal semiconductor channels 59. In otherembodiments, rather than forming the source regions 61 in thesemiconductor material layer 10, a horizontal source layer (e.g., buriedsource layer) which contacts a sidewalls of the semiconductor channelmay be formed as described in U.S. Pat. No. 10,559,582 B1, incorporatedherein by reference in its entirety. In this configuration, thesemiconductor devices 700 (e.g., CMOS devices) for the peripheralcircuitry may be formed under the alternating stack (32, 42) in a CMOSunder array configuration. Alternatively, the semiconductor devices 700(e.g., CMOS devices) for the peripheral circuitry may be formed on aseparate substrate which is then bonded to the memory device in a CMOSbonded to array configuration.

Referring to FIGS. 9A and 9B, an etchant that selectively etches thesecond material of the sacrificial material layers 42 with respect tothe first material of the insulating layers 32 can be introduced intothe backside trenches 79, for example, employing an etch process.Backside recesses 43 are formed in volumes from which the sacrificialmaterial layers 42 are removed. The removal of the second material ofthe sacrificial material layers 42 can be selective to the firstmaterial of the insulating layers 32, the material of the retro-steppeddielectric material portion 65, the semiconductor material of thesemiconductor material layer 10, and the material of the outermost layerof the memory films 50. In one embodiment, the sacrificial materiallayers 42 can include silicon nitride, and the materials of theinsulating layers 32 and the retro-stepped dielectric material portion65 can be selected from silicon oxide and dielectric metal oxides.

The etch process that removes the second material selective to the firstmaterial and the outermost layer of the memory films 50 can be a wetetch process employing a wet etch solution, or can be a gas phase (dry)etch process in which the etchant is introduced in a vapor phase intothe backside trenches 79. For example, if the sacrificial materiallayers 42 include silicon nitride, the etch process can be a wet etchprocess in which the first exemplary structure is immersed within a wetetch tank including phosphoric acid, which etches silicon nitrideselective to silicon oxide, silicon, and various other materialsemployed in the art. The support pillar structure 20, the retro-steppeddielectric material portion 65, and the memory stack structures 55provide structural support while the backside recesses 43 are presentwithin volumes previously occupied by the sacrificial material layers42.

Each backside recess 43 can be a laterally extending cavity having alateral dimension that is greater than the vertical extent of thecavity. In other words, the lateral dimension of each backside recess 43can be greater than the height of the backside recess 43. A plurality ofbackside recesses 43 can be formed in the volumes from which the secondmaterial of the sacrificial material layers 42 is removed. The memoryopenings in which the memory stack structures 55 are formed are hereinreferred to as front side openings or front side cavities in contrastwith the backside recesses 43. In one embodiment, the memory arrayregion 100 comprises an array of monolithic three-dimensional NANDstrings having a plurality of device levels disposed above the substrate(9, 10). In this case, each backside recess 43 can define a space forreceiving a respective word line of the array of monolithicthree-dimensional NAND strings.

Each of the plurality of backside recesses 43 can extend substantiallyparallel to the top surface of the substrate (9, 10). A backside recess43 can be vertically bounded by a top surface of an underlyinginsulating layer 32 and a bottom surface of an overlying insulatinglayer 32. In one embodiment, each backside recess 43 can have a uniformheight throughout.

Referring to FIG. 10A, physically exposed surface portions of theoptional pedestal channel portions 11 and the semiconductor materiallayer 10 can be converted into dielectric material portions by thermalconversion and/or plasma conversion of the semiconductor materials intodielectric materials. For example, thermal conversion and/or plasmaconversion can be employed to convert a surface portion of each pedestalchannel portion 11 into a tubular dielectric spacer 116, and to converteach physically exposed surface portion of the semiconductor materiallayer 10 into a planar dielectric portion 616. In one embodiment, eachtubular dielectric spacer 116 can be topologically homeomorphic to atorus, i.e., generally ring-shaped. As used herein, an element istopologically homeomorphic to a torus if the shape of the element can becontinuously stretched without destroying a hole or forming a new holeinto the shape of a torus. The tubular dielectric spacers 116 include adielectric material that includes the same semiconductor element as thepedestal channel portions 11 and additionally includes at least onenon-metallic element such as oxygen and/or nitrogen such that thematerial of the tubular dielectric spacers 116 is a dielectric material.In one embodiment, the tubular dielectric spacers 116 can include adielectric oxide, a dielectric nitride, or a dielectric oxynitride ofthe semiconductor material of the pedestal channel portions 11.Likewise, each planar dielectric portion 616 includes a dielectricmaterial that includes the same semiconductor element as thesemiconductor material layer and additionally includes at least onenon-metallic element such as oxygen and/or nitrogen such that thematerial of the planar dielectric portions 616 is a dielectric material.In one embodiment, the planar dielectric portions 616 can include adielectric oxide, a dielectric nitride, or a dielectric oxynitride ofthe semiconductor material of the semiconductor material layer 10.Dopants in the drain regions 63, the source regions 61, and thesemiconductor channels 60 can be activated during the anneal processthat forms the planar dielectric portions 616 and the tubular dielectricspacers 116. Alternatively, an additional anneal process may beperformed to active the electrical dopants in the drain regions 63, thesource regions 61, and the semiconductor channels 60.

Referring to FIG. 10B, a backside blocking dielectric layer 44 can beoptionally formed. The backside blocking dielectric layer 44, ifpresent, comprises a dielectric material that functions as a controlgate dielectric for the control gates to be subsequently formed in thebackside recesses 43. In case the blocking dielectric layer 52 ispresent within each memory opening, the backside blocking dielectriclayer 44 is optional. In case the blocking dielectric layer 52 isomitted, the backside blocking dielectric layer 44 is present.

The backside blocking dielectric layer 44 can be formed in the backsiderecesses 43 and on a sidewall of the backside trench 79. The backsideblocking dielectric layer 44 can be formed directly on horizontalsurfaces of the insulating layers 32 and sidewalls of the memory stackstructures 55 within the backside recesses 43. If the backside blockingdielectric layer 44 is formed, formation of the tubular dielectricspacers 116 and the planar dielectric portion 616 prior to formation ofthe backside blocking dielectric layer 44 is optional. In oneembodiment, the backside blocking dielectric layer 44 can be formed by aconformal deposition process such as atomic layer deposition (ALD). Thebackside blocking dielectric layer 44 can consist essentially ofaluminum oxide. The thickness of the backside blocking dielectric layer44 can be in a range from 1 nm to 15 nm, such as 2 to 6 nm, althoughlesser and greater thicknesses can also be employed.

The dielectric material of the backside blocking dielectric layer 44 canbe a dielectric metal oxide such as aluminum oxide, a dielectric oxideof at least one transition metal element, a dielectric oxide of at leastone Lanthanide element, a dielectric oxide of a combination of aluminum,at least one transition metal element, and/or at least one Lanthanideelement. Alternatively or additionally, the backside blocking dielectriclayer 44 can include a silicon oxide layer. The backside blockingdielectric layer 44 can be deposited by a conformal deposition methodsuch as chemical vapor deposition or atomic layer deposition. Thebackside blocking dielectric layer 44 is formed on the sidewalls of thebackside trenches 79, horizontal surfaces and sidewalls of theinsulating layers 32, the portions of the sidewall surfaces of thememory stack structures 55 that are physically exposed to the backsiderecesses 43, and a top surface of the planar dielectric portion 616. Abackside cavity 79′ is present within the portion of each backsidetrench 79 that is not filled with the backside blocking dielectric layer44.

Referring to FIG. 10C, a metallic barrier layer 46A can be deposited inthe backside recesses 43. The metallic barrier layer 46A includes anelectrically conductive metallic material that can function as adiffusion barrier layer and/or adhesion promotion layer for a metallicfill material to be subsequently deposited. The metallic barrier layer46A can include a conductive metallic nitride material such as TiN, TaN,WN, or a stack thereof, or can include a conductive metallic carbidematerial such as TiC, TaC, WC, or a stack thereof. In one embodiment,the metallic barrier layer 46A can be deposited by a conformaldeposition process such as chemical vapor deposition (CVD) or atomiclayer deposition (ALD). The thickness of the metallic barrier layer 46Acan be in a range from 2 nm to 8 nm, such as from 3 nm to 6 nm, althoughlesser and greater thicknesses can also be employed. In one embodiment,the metallic barrier layer 46A can consist essentially of a conductivemetal nitride such as TiN.

A metal fill material is deposited in the plurality of backside recesses43, on the sidewalls of the at least one the backside trench 79, andover the top surface of the contact-level dielectric layer 73 to form ametallic fill material layer 46B. The metallic fill material can bedeposited by a conformal deposition method, which can be, for example,chemical vapor deposition (CVD), atomic layer deposition (ALD),electroless plating, electroplating, or a combination thereof. In oneembodiment, the metallic fill material layer 46B can consist essentiallyof at least one elemental metal. The at least one elemental metal of themetallic fill material layer 46B can be selected, for example, fromtungsten, cobalt, ruthenium, titanium, and tantalum. In one embodiment,the metallic fill material layer 46B can consist essentially of a singleelemental metal. In one embodiment, the metallic fill material layer 46Bcan be deposited employing a fluorine-containing precursor gas such asWF₆. In one embodiment, the metallic fill material layer 46B can be atungsten layer including a residual level of fluorine atoms asimpurities. The metallic fill material layer 46B is spaced from theinsulating layers 32 and the memory stack structures 55 by the metallicbarrier layer 46A, which is a metallic barrier layer that blocksdiffusion of fluorine atoms therethrough.

A plurality of electrically conductive layers 46 can be formed in theplurality of backside recesses 43, and a continuous electricallyconductive material layer 46L can be formed on the sidewalls of eachbackside trench 79 and over the contact-level dielectric layer 73. Eachelectrically conductive layer 46 includes a portion of the metallicbarrier layer 46A and a portion of the metallic fill material layer 46Bthat are located between a vertically neighboring pair of dielectricmaterial layers such as a pair of insulating layers 32. The continuouselectrically conductive material layer 46L includes a continuous portionof the metallic barrier layer 46A and a continuous portion of themetallic fill material layer 46B that are located in the backsidetrenches 79 or above the contact-level dielectric layer 73.

Each sacrificial material layer 42 can be replaced with an electricallyconductive layer 46. A backside cavity 79′ is present in the portion ofeach backside trench 79 that is not filled with the backside blockingdielectric layer 44 and the continuous electrically conductive materiallayer 46L. A tubular dielectric spacer 116 laterally surrounds apedestal channel portion 11. A bottommost electrically conductive layer46 laterally surrounds each tubular dielectric spacer 116 upon formationof the electrically conductive layers 46.

Referring to FIGS. 11A-11C, the deposited metallic material of thecontinuous electrically conductive material layer 46L is etched backfrom the sidewalls of each backside trench 79 and from above thecontact-level dielectric layer 73, for example, by an isotropic wetetch, an anisotropic dry etch, or a combination thereof. Each remainingportion of the deposited metallic material in the backside recesses 43constitutes an electrically conductive layer 46. Each electricallyconductive layer 46 can be a conductive line structure. Thus, thesacrificial material layers 42 are replaced with the electricallyconductive layers 46.

Each electrically conductive layer 46 can function as a combination of aplurality of control gate electrodes located at a same level and a wordline electrically interconnecting, i.e., electrically shorting, theplurality of control gate electrodes located at the same level. Theplurality of control gate electrodes within each electrically conductivelayer 46 are the control gate electrodes for the vertical memory devicesincluding the memory stack structures 55. In other words, eachelectrically conductive layer 46 can be a word line that functions as acommon control gate electrode for the plurality of vertical memorydevices.

In one embodiment, the removal of the continuous electrically conductivematerial layer 46L can be selective to the material of the backsideblocking dielectric layer 44. In this case, a horizontal portion of thebackside blocking dielectric layer 44 can be present at the bottom ofeach backside trench 79. In another embodiment, the removal of thecontinuous electrically conductive material layer 46L may not beselective to the material of the backside blocking dielectric layer 44or, the backside blocking dielectric layer 44 may not be employed. Theplanar dielectric portions 616 can be removed during removal of thecontinuous electrically conductive material layer 46L. A backside cavity79′ is present within each backside trench 79.

In one embodiment shown in FIG. 11C, outermost surfaces of the blockingdielectric layer 52 within each memory opening 49 can be laterallyoffset from the vertical semiconductor channel within the respectivememory opening 49 by a first lateral distance ld1. The annularhorizontal surface portions of the first interfaces IN1 between theblocking dielectric layer 52 and the insulating layers 32 can bevertically offset from horizontal surface portions of the secondinterfaces IN2 between the electrically conductive layers 46 and theinsulating layers 32. The horizontal surfaces of portions of theinsulating layers 32 which make up the second interfaces IN2 arelaterally offset from the vertical semiconductor channel 60 by a lateraldistance that is greater than the first lateral distance ld1.

Backside blocking dielectric layers 44 can be located between each ofthe electrically conductive layers 46 and a combination of the blockingdielectric layer 52, a respective underlying one of the insulatinglayers 32, and a respective overlying one of the insulating layers 32.

Referring to FIG. 12, an insulating material layer can be formed in thebackside trenches 79 and over the contact-level dielectric layer 73 by aconformal deposition process. Exemplary conformal deposition processesinclude, but are not limited to, chemical vapor deposition and atomiclayer deposition. The insulating material layer includes an insulatingmaterial such as silicon oxide, silicon nitride, a dielectric metaloxide, an organosilicate glass, or a combination thereof. In oneembodiment, the insulating material layer can include silicon oxide. Theinsulating material layer can be formed, for example, by low pressurechemical vapor deposition (LPCVD) or atomic layer deposition (ALD). Thethickness of the insulating material layer can be in a range from 1.5 nmto 60 nm, although lesser and greater thicknesses can also be employed.

If a backside blocking dielectric layer 44 is present, the insulatingmaterial layer can be formed directly on surfaces of the backsideblocking dielectric layer 44 and directly on the sidewalls of theelectrically conductive layers 46. If a backside blocking dielectriclayer 44 is not employed, the insulating material layer can be formeddirectly on sidewalls of the insulating layers 32 and directly onsidewalls of the electrically conductive layers 46.

An anisotropic etch is performed to remove horizontal portions of theinsulating material layer from above the contact-level dielectric layer73 and at the bottom of each backside trench 79. Each remaining portionof the insulating material layer constitutes an insulating spacer 74. Abackside cavity 79′ is present within a volume surrounded by eachinsulating spacer 74. A top surface of the semiconductor material layer10 can be physically exposed at the bottom of each backside trench 79.

An upper portion of the semiconductor material layer 10 that extendsbetween the source region 61 and the plurality of pedestal channelportions 11 constitutes a horizontal semiconductor channel 59 for aplurality of field effect transistors. The horizontal semiconductorchannel 59 is connected to multiple vertical semiconductor channels 60through respective pedestal channel portions 11. The horizontalsemiconductor channel 59 contacts the source region 61 and the pluralityof pedestal channel portions 11. A bottommost electrically conductivelayer 46 provided upon formation of the electrically conductive layers46 within the alternating stack (32, 46) can comprise a select gateelectrode for the field effect transistors. Each source region 61 isformed in an upper portion of the substrate (9, 10). Semiconductorchannels (59, 11, 60) extend between each source region 61 and arespective set of drain regions 63. The semiconductor channels (59, 11,60) include the vertical semiconductor channels 60 of the memory stackstructures 55.

A backside contact via structure 76 can be formed within each backsidecavity 79′. Each contact via structure 76 can fill a respective backsidecavity 79′. The contact via structures 76 can be formed by depositing atleast one conductive material in the remaining unfilled volume (i.e.,the backside cavity 79′) of the backside trench 79. For example, the atleast one conductive material can include a conductive liner 76A and aconductive fill material portion 76B. The conductive liner 76A caninclude a conductive metallic liner such as TiN, TaN, WN, TiC, TaC, WC,an alloy thereof, or a stack thereof. The thickness of the conductiveliner 76A can be in a range from 3 nm to 30 nm, although lesser andgreater thicknesses can also be employed. The conductive fill materialportion 76B can include a metal or a metallic alloy. For example, theconductive fill material portion 76B can include W, Cu, Al, Co, Ru, Ni,an alloy thereof, or a stack thereof.

The at least one conductive material can be planarized employing thecontact-level dielectric layer 73 overlying the alternating stack (32,46) as a stopping layer. If chemical mechanical planarization (CMP)process is employed, the contact-level dielectric layer 73 can beemployed as a CMP stopping layer. Each remaining continuous portion ofthe at least one conductive material in the backside trenches 79constitutes a backside contact via structure 76.

The backside contact via structure 76 extends through the alternatingstack (32, 46), and contacts a top surface of the source region 61. If abackside blocking dielectric layer 44 is employed, the backside contactvia structure 76 can contact a sidewall of the backside blockingdielectric layer 44.

Referring to FIGS. 13A and 13B, additional contact via structures (88,86, 8P) can be formed through the contact-level dielectric layer 73, andoptionally through the retro-stepped dielectric material portion 65. Forexample, drain contact via structures 88 can be formed through thecontact-level dielectric layer 73 on each drain region 63. Word linecontact via structures 86 can be formed on the electrically conductivelayers 46 through the contact-level dielectric layer 73, and through theretro-stepped dielectric material portion 65. Peripheral device contactvia structures 8P can be formed through the retro-stepped dielectricmaterial portion 65 directly on respective nodes of the peripheraldevices.

Referring to FIGS. 1-13B and according to the first embodiment of thepresent disclosure, a memory device comprises an alternating stack ofinsulating layers 32 and electrically conductive layers 46 located overa substrate (9, 10); and a memory stack structure 55 extending throughthe alternating stack (32, 46), wherein the memory stack structure 55comprises a composite charge storage structure (53, 54), a tunnelingdielectric layer 56 located on an inner sidewall of the composite chargestorage structure (53, 54), and a vertical semiconductor channel 60contacting an inner sidewall of the tunneling dielectric layer 56. Thecomposite charge storage structure (53, 54) comprises a vertical stackof discrete tubular charge storage material portions 53 including afirst charge trapping material located at levels of the electricallyconductive layers 46 and vertically spaced apart from each other, and acontinuous charge storage layer 54 including a second charge trappingmaterial extending through a plurality of the electrically conductivelayers 46. The first charge trapping material has a higher charge trapdensity than the second charge trapping material.

In one embodiment, each of the tubular charge storage material portions53 contacts a portion of an outer sidewall of the charge storage layer54. In one embodiment, the entirety of an inner sidewall of the chargestorage layer 54 contacts an outer sidewall of the tunneling dielectriclayer 56.

In one embodiment, the memory device comprises a blocking dielectriclayer 52 that continuously extends through the plurality of electricallyconductive layers 46 and laterally surrounds the composite chargestorage structure (53, 54) and located within a same memory opening 49.

In one embodiment, the blocking dielectric layer 52 compriseslaterally-protruding portions that protrude outward from the compositecharge storage structure (53, 54) at each level of the plurality ofelectrically conductive layers 46. Interfaces IN1 between the blockingdielectric layer 52 and the insulating layers 32 include annularhorizontal surface portions. In one embodiment illustrated in FIG. 11C,the outermost surfaces of the blocking dielectric layer 52 can belaterally offset from the vertical semiconductor channel 60 by a firstlateral distance ld1, and the annular horizontal surface portions of theinterfaces IN1 can be vertically offset from horizontal surfaces ofportions of the insulating layers 32 which form the interfaces IN2 withthe electrically conductive layers 46. The vertical offset distancebetween the annular horizontal surface portions of the interfaces IN1and a most proximal horizontal plane including horizontal surfaces ofportions of the insulating layers 32 of interfaces IN2 (which arelaterally offset from the vertical semiconductor channel 60 by a lateraldistance that is greater than the first lateral distance ld1) can be thesame as the recess distance of the second isotropic etch process of FIG.5D.

In one embodiment, a metal oxide backside blocking dielectric layer 44can be located between the blocking dielectric layer 52 which comprisessilicon oxide and each of the electrically conductive layers 46.

In one embodiment shown in FIG. 11C, an inner sidewall of the blockingdielectric layer 52 comprises insulating-layer-level sidewall segments521L located at levels of the insulating layers 32, and annular recessedsidewall segments 52AR that are located at levels of the plurality ofelectrically conductive layers 46 and laterally recessed outwardrelative to insulating-layer-level sidewall segments. In one embodiment,the tubular charge storage material portions 53 are vertically spacedapart from each other by the insulating-layer-level sidewall segments521L of the blocking dielectric layer 52. In one embodiment, each of thetubular charge storage material portions 53 contacts a respective one ofthe annular recessed sidewall segments 52AR and has a respective innersidewall that is vertically coincident with an overlying one of theinsulating-layer-level sidewall segments 521L of the blocking dielectriclayer 52.

In one embodiment, each inner sidewall of the tubular charge storagematerial portions 53 can be vertically coincident with the segments ofthe inner sidewall of the blocking dielectric layer 52 that are locatedat levels of the insulating layers 32. In one embodiment, the entiretyof an outer sidewall of the charge storage layer 54 can be straight in avertical cross-sectional view that passes through a geometrical centerof the volume of the memory opening fill structure 58.

In one embodiment, the first charge storage material comprises, and/orconsists essentially of, aluminum nitride and the second charge storagematerial comprises, and/or consists essentially of, silicon nitride.

In one embodiment, the alternating stack (32, 46) comprises a terraceregion in which each electrically conductive layer 46 other than atopmost electrically conductive layer 46 within the alternating stack(32, 46) laterally extends farther than any overlying electricallyconductive layer 46 within the alternating stack (32, 46); the terraceregion includes stepped surfaces of the alternating stack (32, 46); andsupport pillar structures 20 extend through the stepped surfaces andthrough a retro-stepped dielectric material portion 65 that overlies thestepped surfaces.

The first embodiment of the present disclosure provides a compositecharge storage structure (53, 54) within each memory opening 49. Eachcomposite charge storage structure (53, 54) includes discrete portions53 of a first charge storage material having a high charge trap densityand high electron mobility at each level of the electrically conductivelayers 46 comprising the tubular charge storage material portions 53.The first charge storage material of the tubular charge storage materialportions 53 provides high programming speed, and stores a high densityof electrical charge (e.g., electrons). The high electron mobility ofthe first charge storage material does not induce high charge leakagewhich degrades data retention because this material is confined indiscrete portions 53 at level of a respective electrically conductivelayer 46. However, if the discrete portions 53 are used alone, then theymay degrade the program slope.

Therefore, a continuous charge storage layer 54 is added at levels ofthe insulating layers 32 and the electrically conductive layers 46 tolink up the discrete portions 53 in the composite charge storagestructure (53, 54) to improve the program slope. The continuous chargestorage layer 54 includes a second charge storage material having alower charge trap density and a lower electron mobility than the firstcharge storage material. As such, electron leakage within the compositecharge storage structure (53, 54) between neighboring memory cells isreduced, and data retention is not significantly degraded by thecontinuous charge storage layer 54. Thus, the composite charge storagestructure (53, 54) can provide both improved programming speed and data(i.e., charge) retention characteristics without degrading the programslope for the memory stack structure 55.

Referring to FIG. 14A, a region of a second exemplary structureaccording to a second embodiment of the present disclosure isillustrated, which illustrates a memory opening 49 extending through analternating stack of insulating layers 32 and sacrificial materiallayers 42. The insulating layers 32 can include silicon oxide, and thesacrificial material layers 42 can include silicon nitride or asilicon-containing material such as amorphous silicon or polysilicon.The second exemplary structure of FIG. 14A can be derived from the firstexemplary structure of FIGS. 4A and 4B by performing the processingsteps of FIG. 5B, i.e., by forming an optional pedestal channel portion(e.g., an epitaxial pedestal) 11 at the bottom portion of each memoryopening 49 and each support openings 19, for example, by selectiveepitaxy. A memory cavity 49′ is present in unfilled volumes of thememory opening 49. FIGS. 14A-14K illustrate structural changes in amemory opening 49, which is one of the memory openings 49 in the secondexemplary structure. The same structural change occurs simultaneously ineach of the other memory openings 49 and in each of the support openings19 in the second exemplary structure.

Referring to FIG. 14B, the sacrificial material layers 42 are laterallyrecessed selective to the insulating layers 32 by an isotropic etchprocess to form annular recess regions 349. The isotropic etch processcan laterally recess sidewalls of the sacrificial material layers 42relative to sidewalls of the insulating layers 32 around each memoryopening 49. In one embodiment, the isotropic etch process may include awet etch process. For example, if the insulating layers 32 include asilicon oxide material and if the sacrificial material layers 42 includesilicon nitride, a wet etch process employing hot phosphoric acid can beemployed to selectively etch the material of the sacrificial materiallayers 42 selective to the material of the insulating layers 32. In casethe sacrificial material layers 42 includes a semiconductor materialsuch as amorphous silicon or polysilicon, a wet etch process using hottrimethyl-2 hydroxyethyl ammonium hydroxide (“hot TMY”) or tetramethylammonium hydroxide (TMAH) may be used to laterally recess thesacrificial material layers 42. In this case, the pedestal channelportion 11 may be collaterally vertically recessed. The annular recessregions 349 are formed around the memory opening 49 at levels of thesacrificial material layers 42 that are located above the horizontalplane including the top surface of the pedestal channel portion 11. Therecessed sidewalls of the sacrificial material layers 42 can becylindrical. The lateral recess distance of the first isotropic etchprocess can be in a range from 10 nm to 100 nm, such as from 20 nm to 50nm, although lesser and greater lateral recess distances can also beemployed.

Referring to FIG. 14C, an oxidation process can be performed to convertsurface portions of the sacrificial material layers 42 that arephysically exposed to the memory cavity 49′ into silicon oxide blockingdielectric portions 152. The surface portions of the sacrificialmaterial layers 42 around the annular recess regions 349 are convertedinto silicon oxide blocking dielectric portions 152. Each of the siliconoxide blocking dielectric portions 152 can have a tubular shape, andcontacts a bottom surface of a respective overlying insulating layer 32and contacts a top surface of a respective underlying insulating layer32. The silicon oxide blocking dielectric portions 152 can be formed ateach level of the sacrificial material layers 42 that are located abovethe horizontal plane including the top surface of the pedestal channelportion 11 as provided at the processing steps of FIG. 14B. The lateralthickness of each silicon oxide blocking dielectric portion 152, asmeasured between an inner sidewall and an outer sidewall, can be in arange from 3 nm to 20 nm, such as from 5 nm to 15 nm, although lesserand greater thicknesses can also be employed.

In case the sacrificial material layers 42 include silicon nitride, thesilicon oxide blocking dielectric portions 152 can include residualnitrogen atoms at outer surface portions such that the atomicconcentration of nitrogen atoms decreases with a lateral distance inward(i.e., toward the memory cavity 49′) from the outer sidewall within eachsilicon oxide blocking dielectric portion 152. In case the sacrificialmaterial layers include amorphous silicon or polysilicon, the siliconoxide blocking dielectric portions 152 can consist essentially ofsilicon oxide and optional dopant atoms (such as boron, phosphorus,and/or arsenic). A sacrificial silicon oxide plate 13 can be formed bycollateral oxidation of a surface portion of the pedestal channelportion 11.

Referring to FIG. 14D, a set of material layers (541L, 542L, 543L) canbe sequentially conformally deposited in the memory cavity 49′ by a setof conformal deposition processes. The set of material layers (541L,542L, 543L) can include an optional silicon nitride material layer 541Lthat is conformally deposited directly on the silicon oxide blockingdielectric portions 152, a silicon carbide nitride (i.e., siliconcarbonitride) material layer 542L that is deposited directly on thesilicon nitride material layer 541L, if present, or directly on thesilicon oxide blocking dielectric portions 152 in case the siliconnitride material layer 541L is omitted, and a silicon nitride fillmaterial layer 543L that is deposited on the silicon carbide nitridematerial layer 542L. The set of material layers (541L, 542L, 543L) isdeposited in the annular recess regions 349 and at peripheral portionsof the memory opening 49 as conformal material layers.

The silicon nitride material layer 541L can consist essentially of astoichiometric or non-stoichiometric silicon nitride. The thickness ofthe silicon nitride material layer 541L can be in a range from 1 nm to 6nm, such as from 2 nm to 4 nm, although lesser and greater thicknessescan also be employed. The silicon nitride material layer 541L can bedeposited by a conformal deposition process such as low pressurechemical vapor deposition (LPCVD). The silicon carbide nitride materiallayer 542L includes a silicon carbide nitride material which containsany suitable non-zero atomic concentration of silicon, carbon andnitrogen, such as at least 5 atomic percent of silicon, carbon andnitrogen. In one embodiment, the atomic percentage of nitrogen atoms isbetween 5% and 20%, such as between 10% and 15%, the atomic percentageof silicon atoms is between 25% and 45%, such as between 30% and 40%,and the atomic percentage of carbon atoms is between 30% and 70%, suchas between 50% and 60%. In one embodiment, the silicon carbide nitridematerial layer 542L may contain only silicon, carbon and nitrogen atomsand unavoidable impurities. In another embodiment, additional atomsother than silicon, carbon and nitrogen may be added at a concentrationof 10 atomic percent or less. The silicon carbide nitride material layer542L can be deposited by a conformal deposition process such as a lowpressure chemical vapor deposition process employing a siliconprecursor, a carbon precursor, and a nitrogen precursor, or by an atomiclayer deposition process in which a silicon nitride deposition processand a carbonization process are repeated performed to provide a siliconcarbide nitride material. The thickness of the silicon carbide nitridematerial layer 542L can be in a range from 1 nm to 10 nm, such as from 2nm to 4 nm, although lesser and greater thicknesses can also beemployed. An unfilled annular volume can be present within each of theannular recess regions 349 after deposition of the silicon carbidenitride material layer 542L.

The silicon nitride fill material layer 543L can consist essentially ofa stoichiometric or non-stoichiometric silicon nitride. The thickness ofthe silicon nitride fill material layer 543L can be selected such thatthe unfilled annular volumes of the annular recess regions 349 afterformation of the silicon carbide nitride material layer 542L are filledwithin the silicon nitride fill material layer 543L. The lateralthickness of the silicon nitride fill material layer 543L at levels ofthe insulating layers 32 can be in a range from 6 nm to 40 nm, such asfrom 10 nm to 25 nm, although lesser and greater thicknesses can also beemployed. The silicon nitride fill material layer 543L can be depositedby a conformal deposition process such as low pressure chemical vapordeposition (LPCVD).

Referring to FIG. 14E, portions of the set of material layers (541L,542L, 543L) located outside the volumes of the annular recess regionscan be etched back by an etch back process. The etch back process mayemploy an isotropic etch process, an anisotropic etch process, or acombination thereof. In one embodiment, an anisotropic etch process suchas a reactive ion etch process can be performed to etch portions of theset of material layers (541L, 542L, 543L) that are not masked by arespective overlying portion of the insulating layers 32. In this case,inner sidewalls of remaining portions of the set of material layers(541L, 542L, 543L) can be vertically coincident with sidewalls of theinsulating layers 32. In another embodiment, an isotropic etch processthat indiscriminately etches the materials of the set of material layers(541L, 542L, 543L) can be performed to remove portions of the set ofmaterial layers (541L, 542L, 543L) located outside the volumes of theannular recess regions 349. Generally, the set of material layers (541L,542L, 543L) can be partly etched back such that portions of the set ofmaterial layers (541L, 542L, 543L) located on sidewalls of theinsulating layers 32 are removed, and the sidewalls of the insulatinglayers 32 are physically exposed around each memory cavity 49′. Thesacrificial silicon oxide plate 13 can be collaterally etched during theetch back process that partially etches the set of material layers(541L, 542L, 543L). For example, if an anisotropic etch process isemployed to remove unmasked portions of the set of material layers(541L, 542L, 543L), the anisotropic etch process can etch thesacrificial silicon oxide plate 13 selective to the pedestal channelportion 11.

Remaining discrete material portions located in the annular recessregions 349 comprise discrete charge storage elements 154. Each discretecharge storage element 154 is a composite charge storage structureincluding multiple materials. Each of the discrete charge storageelements 154 comprises a silicon nitride portion 543, a silicon carbidenitride liner 542, and an optional silicon nitride liner 541. Eachsilicon nitride portion 543 is a remaining portion of the siliconnitride fill material layer 543L. Each silicon carbide nitride liner 542is a remaining portion of the silicon carbide nitride material layer542L. Each silicon nitride liner 541 is a remaining portion of thesilicon nitride material layer 541L.

Each silicon carbide nitride liner 542 can be disposed between arespective silicon nitride portion 543 and a respective sacrificialmaterial layer 42 located at a same level as the silicon nitride portion543. Each silicon carbide nitride liner 542 can have a uniformcomposition throughout. Within each discrete charge storage element 154,the silicon carbide nitride liner 542 contacts a top surface of thesilicon nitride portion 543, an outer sidewall of the silicon nitrideportion 543, and a bottom surface of the silicon nitride portion 543.Within each discrete charge storage element 154, the silicon nitrideliner 541 can contact the silicon carbide nitride liner 542. The siliconnitride liner 541 of each of the discrete charge storage elements 154contacts a respective overlying one of the insulating layers 32, andcontacts a respective underlying one of the insulating layers 32. In oneembodiment, the silicon nitride liner 541 of each of the discrete chargestorage elements 154 contacts an annular horizontal bottom surface ofthe respective overlying one of the insulating layers 32, contacts anannular horizontal top surface of the respective underlying one of theinsulating layers 32, and contacts a cylindrical sidewall of arespective silicon oxide blocking dielectric portion 152. Each of thediscrete charge storage elements 154 can have a respective tubularshape, and can be formed directly on a respective one of the siliconoxide blocking dielectric portions 152. In one embodiment, physicallyexposed cylindrical sidewalls of the discrete charge storage elements154 and cylindrical sidewalls of the insulating layers 32 can bevertically coincident with each other, i.e., can be located within acylindrical plane that vertically extends from the topmost surface ofthe pedestal channel portion to the top surface of the topmostinsulating layer 32T.

Referring to FIG. 14F, a tunneling dielectric layer 56 can be depositedover the inner sidewalls of the discrete charge storage elements 154 andthe physically exposed surfaces of the insulating layers 32. Thetunneling dielectric layer 56 includes a dielectric material throughwhich charge tunneling can be performed under suitable electrical biasconditions. The charge tunneling may be performed through hot-carrierinjection or by Fowler-Nordheim tunneling induced charge transferdepending on the mode of operation of the monolithic three-dimensionalNAND string memory device to be formed. The tunneling dielectric layer56 can include silicon oxide, silicon nitride, silicon oxynitride,dielectric metal oxides (such as aluminum oxide and hafnium oxide),dielectric metal oxynitride, dielectric metal silicates, alloys thereof,and/or combinations thereof. In one embodiment, the tunneling dielectriclayer 56 can include a stack of a first silicon oxide layer, a siliconoxynitride layer, and a second silicon oxide layer, which is commonlyknown as an ONO stack. In one embodiment, the tunneling dielectric layer56 can include a silicon oxide layer that is substantially free ofcarbon or a silicon oxynitride layer that is substantially free ofcarbon. The thickness of the tunneling dielectric layer 56 can be in arange from 2 nm to 20 nm, although lesser and greater thicknesses canalso be employed.

An optional first semiconductor channel layer 601 can be formed on thetunneling dielectric layer 56. The optional first semiconductor channellayer 601 includes a semiconductor material such as at least oneelemental semiconductor material, at least one III-V compoundsemiconductor material, at least one II-VI compound semiconductormaterial, at least one organic semiconductor material, or othersemiconductor materials known in the art. In one embodiment, the firstsemiconductor channel layer 601 includes amorphous silicon orpolysilicon. The first semiconductor channel layer 601 can be formed bya conformal deposition method such as low pressure chemical vapordeposition (LPCVD). The thickness of the first semiconductor channellayer 601 can be in a range from 2 nm to 10 nm, although lesser andgreater thicknesses can also be employed. A memory cavity 49′ is presentin the volume of each memory opening 49.

Referring to FIG. 14G, the optional first semiconductor channel layer601 and the tunneling dielectric layer 56 are sequentiallyanisotropically etched employing at least one anisotropic etch process.The portions of the first semiconductor channel layer 601 and thetunneling dielectric layer 56 located above the top surface of thetopmost insulating layer 32T can be removed by the at least oneanisotropic etch process. Further, the horizontal portions of the firstsemiconductor channel layer 601 and the tunneling dielectric layer 56can be removed to form openings in remaining portions thereof. Each ofthe first semiconductor channel layer 601 and the tunneling dielectriclayer 56 can be etched by a respective anisotropic etch processemploying a respective etch chemistry, which may, or may not, be thesame for the various material layers. Each remaining portion of thefirst semiconductor channel layer 601 can have a tubular configuration.

A surface of the pedestal channel portion 11 (or a surface of thesemiconductor material layer 10 in case the pedestal channel portions 11are not employed) can be physically exposed underneath the openingthrough the first semiconductor channel layer 601 and the tunnelingdielectric layer 56. Optionally, the physically exposed semiconductorsurface at the bottom of each memory cavity 49′ can be verticallyrecessed so that the recessed semiconductor surface underneath thememory cavity 49′ is vertically offset from the topmost surface of thepedestal channel portion 11 (or of the semiconductor material layer 10in case pedestal channel portions 11 are not employed) by a recessdistance. The combination of the vertical stack of silicon oxideblocking dielectric portions 152, the vertical stack of discrete chargestorage elements 154, and the tunneling dielectric layer 56 constitutesa memory film 150.

Referring to FIG. 14H, a second semiconductor channel layer 602 can bedeposited directly on the semiconductor surface of the pedestal channelportion 11 or the semiconductor material layer 10 if the pedestalchannel portion 11 is omitted, and directly on the first semiconductorchannel layer 601. The second semiconductor channel layer 602 includes asemiconductor material such as at least one elemental semiconductormaterial, at least one III-V compound semiconductor material, at leastone II-VI compound semiconductor material, at least one organicsemiconductor material, or other semiconductor materials known in theart. In one embodiment, the second semiconductor channel layer 602includes amorphous silicon or polysilicon. The second semiconductorchannel layer 602 can be formed by a conformal deposition method such aslow pressure chemical vapor deposition (LPCVD). The thickness of thesecond semiconductor channel layer 602 can be in a range from 2 nm to 10nm, although lesser and greater thicknesses can also be employed. Thesecond semiconductor channel layer 602 may partially fill the memorycavity 49′ in each memory opening, or may fully fill the cavity in eachmemory opening.

The materials of the first semiconductor channel layer 601 and thesecond semiconductor channel layer 602 are collectively referred to as asemiconductor channel material. In other words, the semiconductorchannel material is a set of all semiconductor material in the firstsemiconductor channel layer 601 and the second semiconductor channellayer 602.

Referring to FIG. 14I, in case the memory cavity 49′ in each memoryopening is not completely filled by the second semiconductor channellayer 602, a dielectric core layer 62L can be deposited in the memorycavity 49′ to fill any remaining portion of the memory cavity 49′ withineach memory opening. The dielectric core layer 62L includes a dielectricmaterial such as silicon oxide or organosilicate glass. The dielectriccore layer 62L can be deposited by a conformal deposition method such aslow pressure chemical vapor deposition (LPCVD), or by a self-planarizingdeposition process such as spin coating.

Referring to FIG. 14J, the horizontal portion of the dielectric corelayer 62L can be removed, for example, by a recess etch from above thetop surface of the second semiconductor channel layer 602. Further, thematerial of the dielectric core layer 62L can be vertically recessedselective to the semiconductor material of the second semiconductorchannel layer 602 into each memory opening 49 down to a depth between afirst horizontal plane including the top surface of the topmostinsulating layer 32T and a second horizontal plane including the bottomsurface of the topmost insulating layer 32T. Each remaining portion ofthe dielectric core layer 62L constitutes a dielectric core 62.

Referring to FIG. 14K, a doped semiconductor material having a doping ofa second conductivity type can be deposited within each recessed regionabove the dielectric cores 62. The second conductivity type is theopposite of the first conductivity type. For example, if the firstconductivity type is p-type, the second conductivity type is n-type, andvice versa. The dopant concentration of the doped semiconductor materialcan be in a range from 5.0×10¹⁹/cm³ to 2.0×10²¹/cm³, although lesser andgreater dopant concentrations can also be employed. The dopedsemiconductor material can be, for example, doped polysilicon.

Excess portions of the deposited semiconductor material can be removedfrom above the top surface of the topmost insulating layer 32T, forexample, by chemical mechanical planarization (CMP) or a recess etch.Each remaining portion of the semiconductor material having a doping ofthe second conductively type constitutes a drain region 63. Thehorizontal portion of the second semiconductor channel layer 602 locatedabove the top surface of the topmost insulating layer 32T can beconcurrently removed by a planarization process. Each remaining portionof the second semiconductor channel layer 602 can be located entiretywithin a memory opening 49 or entirely within a support opening 19.

Each remaining portion of the doped semiconductor material having adoping of the second conductivity type constitutes a drain region 63.Each adjoining pair of a first semiconductor channel layer 601 and asecond semiconductor channel layer 602 can collectively form a verticalsemiconductor channel 60 through which electrical current can flow whena vertical NAND device including the vertical semiconductor channel 60is turned on. A tunneling dielectric layer 56 is surrounded by avertical stack of discrete charge storage elements 154, and laterallysurrounds a portion of the vertical semiconductor channel 60. Thevertical stack of discrete charge storage elements 154 can store arespective data bit with a macroscopic retention time. As used herein, amacroscopic retention time refers to a retention time suitable foroperation of a memory device as a permanent memory device such as aretention time in excess of 24 hours.

Each combination of a memory film 150 and a vertical semiconductorchannel 60 within a memory opening 49 constitutes a memory stackstructure 155. The memory stack structure 155 is a combination of avertical semiconductor channel 60, a tunneling dielectric layer 56, avertical stack of discrete charge storage elements 154, and a verticalstack of silicon oxide blocking dielectric portions 152. Eachcombination of a pedestal channel portion 11 (if present), a memorystack structure 155, a dielectric core 62, and a drain region 63 withina memory opening 49 is herein referred to as a memory opening fillstructure 58. Each combination of a pedestal channel portion 11 (ifpresent), a memory film 150, a vertical semiconductor channel 60, adielectric core 62, and a drain region 63 within each support opening 19fills the respective support openings 19, and constitutes a supportpillar structure.

Referring to FIG. 15, the processing steps of FIGS. 7A-7C, 8, 9A and 9B,10A-10C, and 11A-11C can be subsequently performed to form acontact-level dielectric layer 73, backside trenches 79, source regions61, backside recesses 43, optional backside blocking dielectric layers44, and electrically conductive layers 46.

Referring to FIG. 16, the processing steps of FIGS. 11, 12A, and 12B canbe performed to form an insulating spacer 74 and a backside contact viastructure 76 in each backside trench 79, and to form various contact viastructures (88, 86, 8P) in the same manner as in the first embodiment.

Referring to FIG. 17, a memory opening fill structure 58 within analternative configuration of the second exemplary structure according toa second embodiment of the present disclosure is illustrated, which canbe derived from the memory opening fill structure 58 of FIG. 14K byomitting formation of the optional silicon nitride material layer 541Lat the processing steps of FIG. 14D. Instead, the silicon carbidenitride material layer 542L is deposited directly on the silicon oxideblocking dielectric portions 152.

Each discrete charge storage element 154 does not include a siliconnitride liner 541 in the alternative configuration of the secondexemplary structure. In this case, the silicon carbide nitride liner 542of each of the discrete charge storage elements 154 contacts arespective overlying one of the insulating layers 32, and contacts arespective underlying one of the insulating layers 32. In oneembodiment, the silicon carbide nitride liner 542 of each of thediscrete charge storage elements 154 contacts an annular horizontalbottom surface of the respective overlying one of the insulating layers32, contacts an annular horizontal top surface of the respectiveunderlying one of the insulating layers 32, and contacts a cylindricalsidewall of a respective silicon oxide blocking dielectric portion 152.

Referring to FIG. 18, the processing steps of FIGS. 7A-7C, 8, 9A and 9B,10A-10C, and 11A-11C can be subsequently performed to form acontact-level dielectric layer 73, backside trenches 79, source regions61, backside recesses 43, optional backside blocking dielectric layers44, and electrically conductive layers 46. Further, the processing stepsof FIGS. 11, 12A, and 12B can be performed to form an insulating spacer74 and a backside contact via structure 76 in each backside trench 79,and to form various contact via structures (88, 86, 8P) in the samemanner as in the first embodiment.

Referring to FIG. 19, a band diagram of a region between an electricallyconductive layer 46 and a vertical semiconductor channel 60 within thesecond exemplary structure of FIG. 16 is illustrated when the externalbias voltage to the electrically conductive layer 46 relative to thevertical semiconductor channel 60 is zero. In the illustrative example,the tunneling dielectric layer 56 can include an ONO stack. The ONOstack can include a first silicon oxide layer, a silicon oxynitridelayer, and a second silicon oxide layer. The discrete charge storageelement 154 includes a stack of a silicon nitride portion 543, a siliconcarbide nitride liner 542, and a silicon nitride liner 541. The siliconcarbide nitride liner 542 has a band gap energy (i.e., the differencebetween the conduction band and the valence band) in a range from 3.3 eVto 3.8 eV depending on the material composition. The silicon carbidenitride liner 542 forms a deeper well than a well formed by a chargestorage element consisting of silicon nitride. This may reduce electronleakage into the electrically conductive layers 46. Better programmingefficiency and a high program slope can be achieved by a discrete chargestorage element 154 including a stack of a silicon nitride portion 543,a silicon carbide nitride liner 542, and a silicon nitride liner 541, orby a discrete charge storage element 154 including a stack of a siliconnitride portion 543 and a silicon carbide nitride liner 542, than acomparative exemplary charge storage element consisting of a singlesilicon nitride material portion.

Without wishing to be bound by a particular theory, it is believed thata significant portion of the electrons is stored in the part of thediscrete charge storage element 154 closer to the blocking dielectricthan to the tunneling dielectric. Therefore, in one embodiment, thesilicon carbide nitride liner 542 with the deeper conduction band wellis provided closer to the blocking dielectric (e.g., the silicon oxideblocking dielectric portions 152) than to the tunneling dielectric 60 toprovide the electron storage well in the location where the significantportion of the electrons is stored. Therefore, if the silicon nitrideliner 541 is present in the discrete charge storage element 154, thenthe silicon nitride liner 541 is thinner than the silicon nitrideportion 543 to form the carbide nitride liner 542 closer to the blockingdielectric than to the tunneling dielectric. For example, the siliconnitride liner 541 is at least 50% thinner, such as 75% to 300% thinnerthan the silicon nitride portion 543.

Referring to FIGS. 14A to 19 and according to the second embodiment ofthe present disclosure, a memory device comprises an alternating stackof insulating layers 32 and electrically conductive layers 46 locatedover a substrate (9, 10), and a memory stack structure 58 extendingthrough the alternating stack (32, 46). The memory stack structure 58comprises a vertical stack of discrete charge storage elements 154 thatare vertically spaced apart from each other and located at levels of theelectrically conductive layers 46, a tunneling dielectric layer 56located on inner sidewalls of the discrete charge storage elements 154,and a vertical semiconductor channel 60 contacting an inner sidewall ofthe tunneling dielectric layer 56. Each of the discrete charge storageelements 154 comprises: a silicon nitride portion 543 including an innersidewall that contacts an outer sidewall of the tunneling dielectriclayer 56; and a silicon carbide nitride liner 542 in contact with thesilicon nitride portion 543.

In one embodiment, the silicon carbide nitride liner 542 contacts a topsurface of the silicon nitride portion 543, an outer sidewall of thesilicon nitride portion 543, and a bottom surface of the silicon nitrideportion 543 within each of the discrete charge storage elements 154. Inone embodiment, each silicon carbide nitride liner 542 has a uniformcomposition throughout.

In one embodiment, edge portions of the silicon carbide nitride liner542 are in contact with the outer sidewall of the tunneling dielectriclayer 56.

In one embodiment, the atomic percentage of nitrogen atoms is between 5%and 20%, such as between 10% and 15%, the atomic percentage of siliconatoms is between 25% and 45%, such as between 30% and 40%, and theatomic percentage of carbon atoms is between 30% and 70%, such asbetween 50% and 60%, in the silicon carbide nitride liner 542.

In one embodiment, the memory device comprises silicon oxide blockingdielectric portions 152 located at each level of the discrete chargestorage elements 154. Each of the discrete charge storage elements 154is laterally spaced from a respective one of the electrically conductivelayers 46 by a respective one of the silicon oxide blocking dielectricportions 152. In one embodiment, each of the silicon oxide blockingdielectric portions 152 has a respective tubular shape, contacts abottom surface of a respective overlying one of the insulating layers32, and contacts a top surface of a respective underlying one of theinsulating layers 32. In one embodiment, each of the silicon oxideblocking dielectric portions 152 contacts the silicon carbide nitrideliner 142.

In one embodiment, the silicon carbide nitride liner 542 of each of thediscrete charge storage elements 154 contacts a respective overlying oneof the insulating layers 32, and contacts a respective underlying one ofthe insulating layers 32. In one embodiment, the silicon carbide nitrideliner 542 of each of the discrete charge storage elements 154 contactsan annular horizontal bottom surface of the respective overlying one ofthe insulating layers 32, contacts an annular horizontal top surface ofthe respective underlying one of the insulating layers 32, and contactsa cylindrical sidewall of a respective silicon oxide blocking dielectricportion 32.

In one embodiment, each of the discrete charge storage elements 154further comprises a silicon nitride liner 541 contacting the siliconcarbide nitride liner 542 and the outer sidewall of the tunnelingdielectric layer 56. In one embodiment, the silicon nitride liner 541 ofeach of the discrete charge storage elements 154 contacts a respectiveoverlying one of the insulating layers 32, and contacts a respectiveunderlying one of the insulating layers 32. In one embodiment, thesilicon nitride liner 541 of each of the discrete charge storageelements 154 is thinner than the silicon nitride portion 543.

In one embodiment, all surfaces of the silicon nitride portion 543 arein contact with the outer sidewall of the tunneling dielectric layer 56or with a respective surface of the silicon carbide nitride liner 542 ineach of the discrete charge storage elements 154. In one embodiment,each of the discrete charge storage elements 154 has a respectivetubular shape; and the outer sidewall of the tunneling dielectric layer56 has a straight vertical profile that extends through, and contacts,each of the discrete charge storage elements 154 in the memory openingfill structure 58.

Although the foregoing refers to particular preferred embodiments, itwill be understood that the disclosure is not so limited. It will occurto those of ordinary skill in the art that various modifications may bemade to the disclosed embodiments and that such modifications areintended to be within the scope of the disclosure. Compatibility ispresumed among all embodiments that are not alternatives of one another.The word “comprise” or “include” contemplates all embodiments in whichthe word “consist essentially of” or the word “consists of” replaces theword “comprise” or “include,” unless explicitly stated otherwise. Wherean embodiment employing a particular structure and/or configuration isillustrated in the present disclosure, it is understood that the presentdisclosure may be practiced with any other compatible structures and/orconfigurations that are functionally equivalent provided that suchsubstitutions are not explicitly forbidden or otherwise known to beimpossible to one of ordinary skill in the art. All of the publications,patent applications and patents cited herein are incorporated herein byreference in their entirety.

What is claimed is:
 1. A memory device comprising: an alternating stackof insulating layers and electrically conductive layers located over asubstrate; and a memory stack structure extending through thealternating stack, wherein the memory stack structure comprises acomposite charge storage structure, a tunneling dielectric layer locatedon an inner sidewall of the composite charge storage structure, and avertical semiconductor channel contacting an inner sidewall of thetunneling dielectric layer, wherein the composite charge storagestructure comprises: a vertical stack of discrete tubular charge storagematerial portions including a first charge trapping material located atlevels of the electrically conductive layers and vertically spaced apartfrom each other; a continuous charge storage layer including a secondcharge trapping material and extending through a plurality of theelectrically conductive layers, wherein the first charge trappingmaterial has a higher charge trap density than the second chargetrapping material; a blocking dielectric layer that continuously extendsthrough the plurality of electrically conductive layers and laterallysurrounding the composite charge storage structure; and a metal oxidebackside blocking dielectric layer is located between the blockingdielectric layer which comprises silicon oxide and each of theelectrically conductive layers.
 2. The memory device of claim 1, whereineach of the tubular charge storage material portions contacts a portionof an outer sidewall of the continuous charge storage layer.
 3. Thememory device of claim 2, wherein an entirety of an inner sidewall ofthe continuous charge storage layer contacts an outer sidewall of thetunneling dielectric layer.
 4. The memory device of claim 1, wherein:the blocking dielectric layer comprises laterally-protruding portionsthat protrude outward from the composite charge storage structure; andinterfaces between the blocking dielectric layer and the insulatinglayers include annular horizontal surface portions.
 5. The memory deviceof claim 1, wherein an inner sidewall of the blocking dielectric layercomprises: insulating-layer-level sidewall segments located at levels ofthe insulating layers; and annular recessed sidewall segments that arelocated at levels of the plurality of electrically conductive layers andlaterally recessed outward relative to insulating-layer-level sidewallsegments.
 6. The memory device of claim 5, wherein the tubular chargestorage material portions are vertically spaced apart from each other bythe insulating-layer-level sidewall segments of the blocking dielectriclayer.
 7. The memory device of claim 5, wherein each of the tubularcharge storage material portions contacts a respective one of theannular recessed sidewall segments and has a respective inner sidewallthat is vertically coincident with an overlying one of theinsulating-layer-level sidewall segments of the blocking dielectriclayer.
 8. The memory device of claim 1, wherein: the first chargestorage material comprises aluminum nitride or a silicon-rich siliconnitride material; and the second charge storage material comprisessilicon nitride.
 9. The memory device of claim 1, wherein: thealternating stack comprises a terrace region in which each electricallyconductive layer other than a topmost electrically conductive layerwithin the alternating stack laterally extends farther than anyoverlying electrically conductive layer within the alternating stack;the terrace region includes stepped surfaces of the alternating stack;and support pillar structures extend through the stepped surfaces andthrough a retro-stepped dielectric material portion that overlies thestepped surfaces.
 10. A method of forming a memory device, comprising:forming an alternating stack of insulating layers and spacer materiallayers over a substrate, wherein the spacer material layers are formedas, or are subsequently replaced with, electrically conductive layers;forming a memory opening through the alternating stack; and forming amemory stack structure by sequentially forming a composite chargestorage structure, a tunneling dielectric layer, and a verticalsemiconductor channel in the memory opening, wherein the compositecharge storage structure is formed by: forming a vertical stack oftubular charge storage material portions including a first chargetrapping material and at levels of the electrically conductive layers asdiscrete material portions that are vertically spaced apart by theinsulating layers; and forming a charge storage layer including a secondcharge trapping material and extending through a plurality ofelectrically conductive layers of the electrically conductive layers;wherein: the charge storage layer comprises silicon nitride; and thetubular charge storage material portions comprise aluminum nitride or asilicon-rich silicon nitride material.
 11. The method of claim 10,wherein the first charge trapping material has a higher charge trapdensity than the second charge trapping material.
 12. The method ofclaim 10, further comprising forming annular recess regions by laterallyrecessing sidewalls of the spacer material layers relative to sidewallsof the insulating layers around the memory opening, wherein the tubularcharge storage material portions are formed within volumes of theannular recess regions.
 13. The method of claim 12, further comprisingforming a blocking dielectric layer on the sidewalls of the insulatinglayers and the spacer material layers by conformally depositing adielectric material, wherein the tubular charge storage materialportions are formed on the blocking dielectric layer.
 14. The method ofclaim 13, further comprising: depositing the first charge trappingmaterial in unfilled volumes of the annular recess regions afterformation of the blocking dielectric layer; and removing portions of thefirst charge trapping material inside a cylindrical volume defined bysidewall segments of the blocking dielectric layer located at levels ofthe insulating layers by performing an anisotropic etch process thatetches the first charge trapping material, wherein remaining portions ofthe first charge trapping material comprise the tubular charge storagematerial portions.
 15. A method of forming a memory device, comprising:forming an alternating stack of insulating layers and spacer materiallayers over a substrate, wherein the spacer material layers are formedas, or are subsequently replaced with, electrically conductive layers;forming a memory opening through the alternating stack; and forming amemory stack structure by sequentially forming a composite chargestorage structure, a tunneling dielectric layer, and a verticalsemiconductor channel in the memory opening, wherein the compositecharge storage structure is formed by: forming a vertical stack oftubular charge storage material portions including a first chargetrapping material and at levels of the electrically conductive layers asdiscrete material portions that are vertically spaced apart by theinsulating layers; and forming a charge storage layer including a secondcharge trapping material and extending through a plurality ofelectrically conductive layers of the electrically conductive layers;and further comprising: forming annular recess regions by laterallyrecessing sidewalls of the spacer material layers relative to sidewallsof the insulating layers around the memory opening, wherein the tubularcharge storage material portions are formed within volumes of theannular recess regions; forming a blocking dielectric layer on thesidewalls of the insulating layers and the spacer material layers byconformally depositing a dielectric material, wherein the tubular chargestorage material portions are formed on the blocking dielectric layer;and isotropically etching a material of the insulating layers afterformation of the annular recess regions and prior to formation of theblocking dielectric layer, wherein annular top surfaces of the spacermaterial layers and annular bottom surfaces of the spacer materiallayers are physically exposed to the annular recess regions.
 16. Amethod of forming a memory device, comprising: forming an alternatingstack of insulating layers and spacer material layers over a substrate,wherein the spacer material layers are formed as, or are subsequentlyreplaced with, electrically conductive layers; forming a memory openingthrough the alternating stack; and forming a memory stack structure bysequentially forming a composite charge storage structure, a tunnelingdielectric layer, and a vertical semiconductor channel in the memoryopening, wherein the composite charge storage structure is formed by:forming a vertical stack of tubular charge storage material portionsincluding a first charge trapping material and at levels of theelectrically conductive layers as discrete material portions that arevertically spaced apart by the insulating layers; and forming a chargestorage layer including a second charge trapping material and extendingthrough a plurality of electrically conductive layers of theelectrically conductive layers; and wherein the spacer material layersare formed as sacrificial material layers, and the method comprises:forming backside recesses by removing the spacer material layersselective to the insulating layers after formation of the memory stackstructure; and forming a combination of a backside blocking dielectriclayer and a respective one of the electrically conductive layers withineach of the backside recesses.
 17. A method of forming a memory device,comprising: forming an alternating stack of insulating layers and spacermaterial layers over a substrate, wherein the spacer material layers areformed as, or are subsequently replaced with, electrically conductivelayers; forming a memory opening through the alternating stack; andforming a memory stack structure by sequentially forming a compositecharge storage structure, a tunneling dielectric layer, and a verticalsemiconductor channel in the memory opening, wherein the compositecharge storage structure is formed by: forming a vertical stack oftubular charge storage material portions including a first chargetrapping material and at levels of the electrically conductive layers asdiscrete material portions that are vertically spaced apart by theinsulating layers; and forming a charge storage layer including a secondcharge trapping material and extending through a plurality ofelectrically conductive layers of the electrically conductive layers;and further comprising: forming a terrace region by patterning thealternating stack, wherein each spacer material layer other than atopmost spacer material layer within the alternating stack laterallyextends farther than any overlying spacer material layers within thealternating stack; forming a retro-stepped dielectric material portionover the terrace region by depositing a dielectric material over theterrace region; and forming support pillar structures through theretro-stepped dielectric material portion and portions of thealternating stack that underlie the retro-stepped dielectric materialportion.